lavf: remove the pointless value field from flv and iv8

The demuxers don't use it in any way.

libavformat/flvdec.c

@@ -672,5 +672,4 @@ AVInputFormat ff_flv_demuxer = {
 #endif
     .read_close = flv_read_close,
     .extensions = "flv",
-    .value = CODEC_ID_FLV1,
 };

libavformat/iv8.c

@@ -115,5 +115,4 @@ AVInputFormat ff_iv8_demuxer = {
     .read_header    = read_header,
     .read_packet    = read_packet,
     .flags= AVFMT_GENERIC_INDEX,
-    .value = CODEC_ID_MPEG4,
 };