avcodec/h261dec: Remove parse_context cruft

The H.261 decoder doesn't use the ParseContext of its
MpegEncContext since e731697665.

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/h261dec.c

@@ -608,10 +608,7 @@ retry:
     }
 
     if (s->width != avctx->coded_width || s->height != avctx->coded_height) {
-        ParseContext pc = s->parse_context; // FIXME move this demuxing hack to libavformat
-        s->parse_context.buffer = 0;
         ff_mpv_common_end(s);
-        s->parse_context = pc;
     }
 
     if (!s->context_initialized) {