Fix kotlin-gradle-plugin to correctly process java source files

Do not remove outdirectory from cp in maven: this is needed for gradle-plugin build to see files compiled by gmaven
    this may cause problems with running mvn install without clean for kotlin
Remove special magic with groovy-output in gradle-plugin pom.xml

libraries/tools/kotlin-maven-plugin/src/main/java/org/jetbrains/kotlin/maven/K2JVMCompileMojo.java

@@ -104,9 +104,6 @@ public class K2JVMCompileMojo extends KotlinCompileMojoBase<K2JVMCompilerArgumen
         }
 
         ArrayList<String> classpathList = new ArrayList<String>(classpath);
-        if (classpathList.remove(output)) {
-            LOG.debug("Removed target directory from compiler classpath (" + output + ")");
-        }
 
         if (!classpathList.isEmpty()) {
             String classPathString = join(classpathList, File.pathSeparator);