chore(auth, content, settings): Remove SP2 backend API code

[xlisachan]

This pull request

• Removes the following routes/handlers:

  • /v1/oauth/subscriptions/active/new
  • /v1/oauth/subscriptions/active/new-paypal
  • /v1/oauth/subscriptions/customer
  • /v1/oauth/subscriptions/coupon
  • /v1/oauth/subscriptions/coupon/apply
  • /v1/oauth/subscriptions/reactivate
  • /v1/oauth/subscriptions/setupintent/create
  • /v1/oauth/subscriptions/paymentmethod/default
  • /v1/oauth/subscriptions/paymentmethod/failed/detach
  • /v1/oauth/subscriptions/paymentmethod/billing-agreement
  • /v1/oauth/subscriptions/paypal-checkout
  • /v1/oauth/subscriptions/invoice/retry
  • /v1/oauth/subscriptions/invoice/preview
  • /v1/oauth/subscriptions/invoice/preview-subsequent
  • /v1/oauth/subscriptions/productname
  • /v1/oauth/subscriptions/active/{subscriptionId}
  • /v1/oauth/mozilla-subscriptions/customer/plan-eligibility/{planId}

• Removes dead code:
  Payment layer methods (lib/payments/stripe.ts):

  • createPlainCustomer — only called by removed createCustomer handler
  • createSubscriptionWithPMI — only called by removed route handler
  • createSubscriptionWithPaypal — only called by removed route handler
  • postSubscriptionCreationUpdates — only called by above two
  • retryInvoiceWithPaymentId — only called by removed retryInvoice handler
  • previewInvoice — only called by removed route handler
  • retrieveCouponDetails — only called by removed route handler
  • findValidPromoCode — only called by removed extractPromotionCode
  • updateDefaultPaymentMethod — only called by removed route handler
  • removeSources — only called by removed route handler
  • detachPaymentMethod — only called by removed route handler
  • reactivateSubscriptionForCustomer — only called by removed route handler
  • createSetupIntent — only called by removed route handler
  • changeSubscriptionPlan — only called by removed updateSubscription handler
  • cancelSubscriptionForCustomer — only called by removed deleteSubscription handler
  • subscriptionForCustomer — only called by removed handlers
  • setCustomerLocation — only called by removed handler
  • moment import — unused after method removals

Route handler methods (lib/routes/subscriptions/stripe.ts):

• extractPromotionCode — only called by removed handlers
• customerChanged — only called by removed handlers
• getSubscriptionsForSupport — pre-existing dead code (orphaned since 2021 refactor)
• PromotionCodeManager field + import — only used by removed handlers
• Various unused imports (assertNotNull, SubscriptionChangeEligibility, SubscriptionEligibilityResult,
  filterCustomer, filterInvoice, filterIntent, filterSubscription, DeepPartial, couponDTO, invoiceDTO,
  SeverityLevel, Sentry, COUNTRIES_LONG_NAME_TO_SHORT_NAME_MAP, addressLookupCountries, buildTaxAddress,
  deleteAccountIfUnverified, generateIdempotencyKey, METRICS_CONTEXT_SCHEMA, reportSentryMessage,
  reportSentryError, CustomerError, stripeInvoiceToFirstInvoicePreviewDTO,
  stripeInvoicesToSubsequentInvoicePreviewsDTO, getAccountCustomerByUid, SubscriptionUpdateEligibility)

PayPal handler (lib/routes/subscriptions/paypal.ts):

• getCheckoutToken, updatePaypalBillingAgreement, createSubscriptionWithPaypal,
  _createPaypalBillingAgreementAndSubscription, _createPaypalSubscription, processInvoiceInBackground,
  createAndVerifyBillingAgreement, paypalRoutes export
• Various unused imports (filterSubscription, filterCustomer, getMinimumAmount, hasPaypalSubscription,
  createPayPalBA, error, reportSentryError, msToSec, deleteAccountIfUnverified, SubscriptionEligibilityResult,
  buildTaxAddress, DESCRIPTIONS, validators, Stripe, isA, ServerRoute)

PayPal helper (lib/payments/paypal/helper.ts):

• getCheckoutToken — only called by removed route handler
• parseIdempotencyKey — no callers
• createBillingAgreement — only called by removed route handler
• CreateBillingAgreementOptions import

Entire files deleted:

• lib/payments/utils.ts — all exports dead (generateIdempotencyKey, roundTime, sortClientCapabilities,
  clientIdFromMetadataKey, capabilitiesFromMetadataValue, clientIdCapabilityMapFromMetadata)
• lib/payments/utils.spec.ts
• lib/routes/subscriptions/paypal.spec.ts

Stripe formatter (lib/payments/stripe-formatter.ts):

• stripeInvoicesToSubsequentInvoicePreviewsDTO — only called by removed route handler

Shared DTO (fxa-shared/dto/auth/payments/invoice.ts):

• SubsequentInvoicePreview interface
• subsequentInvoicePreviewsSchema const
• subsequentInvoicePreview type
• subsequentInvoicePreviewsSchema type

Validators (lib/routes/validators.js):

• stripePaymentMethodId, paypalPaymentToken, subscriptionPaymentCountryCode
• subscriptionsSetupIntent, subscriptionsSubscriptionExpandedValidator,
  subscriptionsInvoicePIExpandedValidator
• subscriptionsStripeIntentValidator, subscriptionsStripeSourceValidator, subscriptionsStripeInvoiceValidator
• subscriptionsStripePriceValidator, subscriptionsStripeSubscriptionItemValidator,
  subscriptionsStripeSubscriptionValidator
• subscriptionsStripeCustomerValidator
• subscriptionsPaymentToken, subscriptionsSubscriptionListValidator, subscriptionsCustomerValidator

Route utils (lib/routes/subscriptions/utils.ts):

• handleUidAuth — no callers

Test clients:

• reactivateSubscription in test/client/api.js and test/client/index.js
• cancelSubscription in test/client/api.js and test/client/index.js
• reactivateSubscription and cancelSubscription in test/mocks.js

From external packages:

• fxa-auth-client: getProductInfo method
• fxa-content-server: fetchSubscriptionProductName, SUBSCRIPTION_PRODUCT_ROUTE_RE, xhr/sinon imports in test
• fxa-settings: useProductInfoState made no-op

Test spec dead imports (various):

• stripe.spec.ts (routes): Sentry, sentryModule, STRIPE_PRICE_METADATA, CustomerError, uuidv4,
  getAccountCustomerByUidStub, deleteAccountIfUnverifiedStub, stripeInvoiceToFirstInvoicePreviewDTO,
  stripeInvoicesToSubsequentInvoicePreviewsDTO, filterCustomer, filterSubscription, filterInvoice,
  filterIntent, openInvoice, invoicePreviewTax, paymentMethodFixture, newSetupIntent, accountUtils
• stripe.spec.ts (payments): generateIdempotencyKey, roundTime, newCustomerPM, subscriptionPMIExpanded,
  subscriptionPMIExpandedIncompleteCVCFail, newSetupIntent, invoiceRetry, paymentMethodAttach
• mozilla.spec.ts: MozillaSubscriptionHandler, SubscriptionManagementPriceMappingError
• stripe.spec.ts (payments): configuration: null → null as any (pre-existing type fix)

Issue that this pull request solves

Closes: PAY-3617

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• If applicable, I have modified or added tests which pass locally.