avcodec/jpeglsenc: Remove redundant av_packet_unref()

If encoding fails, the AVPacket that ought to contain the encoded packet
is already unreferenced generically.
Reviewed-by: NPaul B Mahol <onemda@gmail.com>
Signed-off-by: NAndreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/jpeglsenc.c

@@ -418,7 +418,6 @@ FF_ENABLE_DEPRECATION_WARNINGS
     return 0;
 
 memfail:
-    av_packet_unref(pkt);
     av_freep(&buf2);
     av_freep(&state);
     av_freep(&zero);