remove custom code
update CFLAGS and ffmpeg/config.asm and ffmpeg/config.h
update ffmpeg (n0.8-19561-gc31458c)

Notes: broken atm because our custom files need to be updated too

* libavcodec/h264_dxva.c
* libavcodec/h264_recov.c
* libavcodec/vc1_dxva.c