avcodec/snow: Remove outdated assert

It comes from a time before frames were refcounted; it has indeed been
added in a follow-up commit to c13e490dce1a66d79e1f053d8a38fb9b2eb53267:
"codec_release_buffer: fix handling of non user buffers". This type
of check is obsolete now.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/snow.c

@@ -566,9 +566,6 @@ av_cold void ff_snow_common_end(SnowContext *s)
     av_freep(&s->emu_edge_buffer);
 
     for(i=0; i<MAX_REF_FRAMES; i++){
-        if(s->last_picture[i] && s->last_picture[i]->data[0]) {
-            av_assert0(s->last_picture[i]->data[0] != s->current_picture->data[0]);
-        }
         av_frame_free(&s->last_picture[i]);
     }