libstagefright: Move OpusHeader files to libstagefright_foundation

Now OpusHeader.cpp is part of libstagefright_foundation.
This avoids a need to include libstagefright_opus_common as an
additional shared library

Bug: 115576456
Test: Tested with a Ogg writer using a local AMediaMuxer
 based application

Change-Id: I102492676447c9f3677e2d418bd39d274ad4f392