remove Plugin-Module manifest entry

THe manifest entry was not correctly caclulated, being different
depending on where you ran maven from and if you also had any local
aggrgator project or not.

The original intention and need of this was to use the path from the git
repostory for the PCT, but the code changed from using a git path along
the way.

As a result the code produced non deterministic results and the PCT
which needed this information has been updated to not need this in jenkinsci/plugin-compat-tester#557

because the information is non deterministic and there are no consumers
of this, it is simpler to remove the code.

src/it/metadata-it/verify.groovy

@@ -37,7 +37,6 @@ try (JarFile j1 = new JarFile(p1)) {
     assert attributes.getValue('Plugin-ScmConnection').equals('scm:git:https://github.com/jenkinsci/maven-hpi-plugin.git')
     def matcher = attributes.getValue('Plugin-GitHash') =~ pattern
     assert matcher.matches()
-    assert attributes.getValue('Plugin-Module').equals('plugin1')
 }
 
 
@@ -71,8 +70,6 @@ try (JarFile j2 = new JarFile(p2)) {
     assert attributes.getValue('Plugin-ScmConnection').equals('scm:git:https://github.com/jenkinsci/maven-hpi-plugin.git')
     def matcher = attributes.getValue('Plugin-GitHash') =~ pattern
     assert matcher.matches()
-    assert attributes.getValue('Plugin-Module').equals('plugin2')
-
 }
 
 return true;

src/it/verify-it/verify.groovy

@@ -58,7 +58,6 @@ Files.newInputStream(new File(basedir, 'target/verify-it/META-INF/MANIFEST.MF').
   assert manifest.getMainAttributes().getValue('Plugin-ScmUrl').equals('https://github.com/jenkinsci/verify-it-plugin')
   def matcher = manifest.getMainAttributes().getValue('Plugin-GitHash') =~ pattern
   assert matcher.matches()
-  assert manifest.getMainAttributes().getValue('Plugin-Module') == null
   assert manifest.getMainAttributes().getValue('Plugin-Version').startsWith('1.0-SNAPSHOT')
   assert manifest.getMainAttributes().getValue('Short-Name').equals('verify-it')
   assert manifest.getMainAttributes().getValue('Specification-Title').equals('MyNewPlugin') // was project.description in previous versions, now project.name

src/main/java/org/jenkinsci/maven/plugins/hpi/AbstractJenkinsManifestMojo.java

@@ -237,7 +237,6 @@ protected void setAttributes(Manifest.ExistingSection mainSection)
         String gitHash = getGitHeadSha1();
         // Deprecated: Use "Implementation-Build" for consistency with core and core components
         addAttributeIfNotNull(mainSection, "Plugin-GitHash", gitHash);
-        addAttributeIfNotNull(mainSection, "Plugin-Module", getModule());
         addAttributeIfNotNull(mainSection, "Implementation-Build", gitHash);
     }