vndk-def: Don't remove all deps in normalization.

This commit no longer removes all dependencies (including system and
vendor dependencies) when a generic reference library has a dependency
to a library on the vendor partition.  After this commit is merged,
vndk_definition_tool.py will only remove the offending dependencies.

Test: Run vndk_definition_tool.py against bullhead build with tweaked
dependencies.

Change-Id: Id6d23112128d9bbfec9e1e4430677a07f20fd193