avfilter/fifo: Remove unused functions and headers
The functions were forgotten in
03c8fe49ea3f2a2444607e541dff15a1ccd7f0c2;
removing them also means that the avassert.h and samplefmt.h headers are
no longer used any more, so they have been removed, too.
Moreover, video.h is unused since
b077d8d9082d057d4c7abd9e0b1a98f9651cfaa8
and channel_layout.h is since
fdd9663781e3ebc8ebed0704607abd174095a905.
Both headers have therefore been removed, too.
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>