Remove avserver.

It has not been properly maintained for years and there is little hope
of that changing in the future.
It appears simpler to write a new replacement from scratch than
unbreaking it.

libavformat/allformats.c

@@ -100,7 +100,6 @@ void av_register_all(void)
     REGISTER_DEMUXER (EA_CDATA,         ea_cdata);
     REGISTER_MUXDEMUX(EAC3,             eac3);
     REGISTER_MUXER   (F4V,              f4v);
-    REGISTER_MUXDEMUX(FFM,              ffm);
     REGISTER_MUXDEMUX(FFMETADATA,       ffmetadata);
     REGISTER_MUXDEMUX(FILMSTRIP,        filmstrip);
     REGISTER_MUXDEMUX(FLAC,             flac);