Remove some stray unnecessary ffmpeg references.

libavcodec/dvbsub.c

libavcodec/dvbsubdec.c

libavcodec/dvdsub_parser.c

libavcodec/dvdsubdec.c

libavcodec/dvdsubenc.c

libavcodec/h263.c

libavcodec/indeo3.c

libavcodec/indeo3data.h

libavcodec/msmpeg4.c

libavcodec/msmpeg4.h

libavcodec/msmpeg4data.c

libavcodec/msmpeg4data.h

libavfilter/vf_drawtext.c

libavformat/avio.c

libavformat/aviobuf.c

libavformat/avisynth.c

libavformat/file.c

libavformat/mpegts.c

libavformat/os_support.c

libavformat/os_support.h