avcodec/vc1_block: Remove redundant write

vc1_decode_skip_blocks() is only called if the current picture
is a P frame. So setting pict_type to AV_PICTURE_TYPE_P
is redundant; removing it makes pict_type read-only in vc1_block.c
(as it should be).

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

libavcodec/vc1_block.c

@@ -2977,7 +2977,6 @@ static void vc1_decode_skip_blocks(VC1Context *v)
         memcpy(s->dest[2], s->last_picture.f->data[2] + s->mb_y *  8 * s->uvlinesize, s->uvlinesize *  8);
         s->first_slice_line = 0;
     }
-    s->pict_type = AV_PICTURE_TYPE_P;
 }
 
 void ff_vc1_decode_blocks(VC1Context *v)