libgsm: remove dupe assigment.

Signed-off-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libgsm.c

@@ -72,7 +72,6 @@ static av_cold int libgsm_encode_init(AVCodecContext *avctx) {
     }
 
     avctx->coded_frame= avcodec_alloc_frame();
-    avctx->coded_frame->key_frame= 1;
     if (!avctx->coded_frame)
         goto error;