Remove non-idiomatic inheritance

Remove inheritance implemented with the bad "superclass calls
subclass through interface" pattern, and replace it with composition.

Test: builds
Change-Id: If323f89360455b3f98b40777edaaaa265bb3b5fc
diff --git a/java/gen.go b/java/gen.go
index e3973bf..e473859 100644
--- a/java/gen.go
+++ b/java/gen.go
@@ -84,7 +84,7 @@
 	return javaFile
 }
 
-func (j *javaBase) genSources(ctx android.ModuleContext, srcFiles android.Paths,
+func (j *Module) genSources(ctx android.ModuleContext, srcFiles android.Paths,
 	flags javaBuilderFlags) android.Paths {
 
 	for i, srcFile := range srcFiles {