[MNG-4945] Remove mergeId from public POM

o Extended ITs to ensure field gets still accepted as part of potentially bad POMs from the repo

git-svn-id: https://svn.apache.org/repos/asf/maven/core-integration-testing/trunk@1050720 13f79535-47bb-0310-9956-ffa450edef68

its/core-it-suite/src/test/resources/mng-4403/repo/org/apache/maven/its/mng4403/b/0.1/b-0.1.pom

@@ -131,6 +131,13 @@ under the License.
   </pluginRepositories>
 
   <build>
+    <resources>
+      <resource>
+        <directory>src/main/resources</directory>
+        <!-- internal field (MNG-4945) -->
+        <mergeId>bad</mergeId>
+      </resource>
+    </resources>
     <plugins>
       <plugin>
         <groupId>org.apache.maven.its.mng4405</groupId>