Fix classes.jack extraction from platform.zip

The copy is handled by the common rule, so JAVA_dependency_template
really only needs to add the extra dependencies. Otherwise we were
getting duplicate rule warnings.

This may extract more files than necessary, but that's better than not
enough.

Bug: 26510884
Change-Id: I022f3cc6ddd1982af3f948740917ac03e795f4c5