lavc/codec_desc.c: remove AV_CODEC_PROP_TEXT_SUB property from ARIB_CAPTION

To support bitmap subtitle output, remove AV_CODEC_PROP_TEXT_SUB
property from codec descriptor for AV_CODEC_ID_ARIB_CAPTION.
This is similar to `libavcodec/libzvbi-teletextdec.c`
(AV_CODEC_ID_DVB_TELETEXT).

Instead, each subtitle decoder has to specify a subtitile format.
`libavcodec/libaribb24.c` uses same AV_CODEC_ID_ARIB_CAPTION and
expects AV_CODEC_PROP_TEXT_SUB to be set, so this adds a line to
specify a format there.

Signed-off-by: rcombs <rcombs@rcombs.me>

libavcodec/codec_desc.c

@@ -3550,7 +3550,6 @@ static const AVCodecDescriptor codec_descriptors[] = {
         .type      = AVMEDIA_TYPE_SUBTITLE,
         .name      = "arib_caption",
         .long_name = NULL_IF_CONFIG_SMALL("ARIB STD-B24 caption"),
-        .props     = AV_CODEC_PROP_TEXT_SUB,
         .profiles  = NULL_IF_CONFIG_SMALL(ff_arib_caption_profiles),
     },
 

libavcodec/libaribb24.c

@@ -291,6 +291,7 @@ next_region:
         av_log(avctx, AV_LOG_DEBUG, "Styled ASS line: %s\n",
                buf.str);
 
+        sub->format = 1; /* text */
         ret = ff_ass_add_rect(sub, buf.str, b24->read_order++,
                               0, NULL, NULL);
     }