avfilter/vf_subtitles, fftools/ffmpeg: Don't set sub_text_format

Unnecessary since 1f63665ca5, because
the value the option is set to coincides with the default value.

Found-by: Soft Works <softworkz@hotmail.com>
Reviewed-by: Soft Works <softworkz@hotmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

fftools/ffmpeg.c

@@ -2991,8 +2991,6 @@ FF_ENABLE_DEPRECATION_WARNINGS
                 av_log(NULL, AV_LOG_WARNING, "Warning using DVB subtitles for filtering and output at the same time is not fully supported, also see -compute_edt [0|1]\n");
         }
 
-        av_dict_set(&ist->decoder_opts, "sub_text_format", "ass", AV_DICT_DONT_OVERWRITE);
-
         /* Useful for subtitles retiming by lavf (FIXME), skipping samples in
          * audio, and video decoders such as cuvid or mediacodec */
         ist->dec_ctx->pkt_timebase = ist->st->time_base;

libavfilter/vf_subtitles.c

@@ -395,7 +395,6 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
     }
     if (ass->charenc)
         av_dict_set(&codec_opts, "sub_charenc", ass->charenc, 0);
-    av_dict_set(&codec_opts, "sub_text_format", "ass", 0);
 
     dec_ctx = avcodec_alloc_context3(dec);
     if (!dec_ctx) {