lavf: Remove codec_tag from dashenc and smoothstreamingenc

Skip the codec_tag altogether here, to let the user (try to) set
whichever codec/tag is preferred; the individual chained muxer will
reject invalid codecs anyway.

(cherry picked from commit 61f589e31e84ae02d7ac6837f30f19c437b1fc2e)
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

libavformat/dashenc.c

@@ -1089,7 +1089,6 @@ AVOutputFormat ff_dash_muxer = {
     .write_packet   = dash_write_packet,
     .write_trailer  = dash_write_trailer,
     .deinit         = dash_free,
-    .codec_tag      = (const AVCodecTag* const []){ ff_mp4_obj_type, 0 },
     .check_bitstream = dash_check_bitstream,
     .priv_class     = &dash_class,
 };

libavformat/smoothstreamingenc.c

@@ -647,6 +647,5 @@ AVOutputFormat ff_smoothstreaming_muxer = {
     .write_header   = ism_write_header,
     .write_packet   = ism_write_packet,
     .write_trailer  = ism_write_trailer,
-    .codec_tag      = (const AVCodecTag* const []){ ff_mp4_obj_type, 0 },
     .priv_class     = &ism_class,
 };