Convert merged srcjar rule to Android.bp

api.go was made to create modules that were hard to create in
Android.bp. However since we now have a filegroup with all the
public srcjars this rule can very easily be expressed in Android.bp.

Test: build before & after (no diff)
Change-Id: I1d6c6bdcd6b75693de1e80ced13efd1d10202171