avcodec/mjpeg2jpeg_bsf: Remove unnecessary header

libavutil/mem.h is unneeded since 33d18982fa,
the commit that introduced the new packet-based bsf API, because with
this switch the allocations were no longer performed directly, but by
av_new_packet().

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/mjpeg2jpeg_bsf.c

@@ -27,7 +27,6 @@
 #include <string.h>
 
 #include "libavutil/error.h"
-#include "libavutil/mem.h"
 #include "libavutil/intreadwrite.h"
 
 #include "avcodec.h"