avcodec/decode: Remove outdated comment

Removing it was forgotten in 417d473bde.

Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/decode.c

@@ -299,7 +299,6 @@ static inline int decode_simple_internal(AVCodecContext *avctx, AVFrame *frame,
     AVCodecInternal   *avci = avctx->internal;
     DecodeSimpleContext *ds = &avci->ds;
     AVPacket           *pkt = ds->in_pkt;
-    // copy to ensure we do not change pkt
     int got_frame, actual_got_frame;
     int ret;