remove invalid free() forgotten in r12300

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@12303 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/imgresample.c

@@ -557,7 +557,6 @@ void sws_freeContext(struct SwsContext *ctx)
     } else {
         av_free(ctx->resampling_ctx);
     }
-    av_free(ctx->av_class);
     av_free(ctx);
 }