Rename Android.soong.mk to Android.mk

Soong is always on now, so we don't have to distinguish between
makefiles that should be ignored because Soong is handling them with an
Android.bp file, and makefiles that are still needed with Soong.  All
obsolete Android.mk files have been removed, rename all Android.soong.mk
files to Android.mk.

Change-Id: Iabbddcbfb2c837cfd4556241b570474452cc5d4d