avcodec/Makefile: Remove FLAC dependencies on vorbis_data
2ef2496cd19eb833f4ad22a5051c11be80d09598 used ff_vorbis_channel_layouts
in flac.c, but added a dependency to the FLAC decoder only; lateron
aba0278e9fe8e66c078588efe66f6af4db432770 added the dependency of the
FLAC parser and encoder on vorbis_data.o. Yet when the original commit
was reverted in
aba0278e9fe8e66c078588efe66f6af4db432770, the two other
dependencies were not removed. This commit fixes this.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>