fix(build): duplicate maven-enforcer-plugin declaration

[c-dilks]

fixes

[WARNING] 
[WARNING] Some problems were encountered while building the effective model for org.jlab.clas:common-tools:pom:13.7.1-SNAPSHOT
[WARNING] 'build.plugins.plugin.(groupId:artifactId)' must be unique but found duplicate declaration of plugin org.apache.maven.plugins:maven-enforcer-plugin @ org.jlab.clas:coatjava:13.7.1-SNAPSHOT, /home/dilks/j/coatjava/pom.xml, line 392, column 15
[WARNING] 
[WARNING] Some problems were encountered while building the effective model for org.jlab.clas:coatjava:pom:13.7.1-SNAPSHOT
[WARNING] 'build.plugins.plugin.(groupId:artifactId)' must be unique but found duplicate declaration of plugin org.apache.maven.plugins:maven-enforcer-plugin @ line 392, column 15
[WARNING] 
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING] 
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]