Remove Android.bp logic from makefiles

When Soong was optional, the make build system needed extra complexity
to ignore Android.mk files that had an associated Android.bp file.  Now
that Soong is required and the Android.mk files that were obsoleted by
an associated Android.bp file have been removed, remove all of the logic
that found associated Android.bp files.  Android.mk files and Android.bp
files are now handled independently.

Change-Id: Ia6643d151b920689219ca8abd59ede44d230ba35