Remove unused variable mb_xy.

Patch by avcoder, ffmpeg gmail

Originally committed as revision 21945 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -981,7 +981,6 @@ static inline void xchg_mb_border(H264Context *h, uint8_t *src_y, uint8_t *src_c
     MpegEncContext * const s = &h->s;
     int deblock_left;
     int deblock_top;
-    int mb_xy;
     int top_idx = 1;
     uint8_t *top_border_m1;
     uint8_t *top_border;