avcodec/gif: remove flags from gifimage option

It does not belong there.

libavcodec/gif.c

@@ -472,7 +472,7 @@ static const AVOption gif_options[] = {
     { "gifflags", "set GIF flags", OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = GF_OFFSETTING|GF_TRANSDIFF}, 0, INT_MAX, FLAGS, "flags" },
         { "offsetting", "enable picture offsetting", 0, AV_OPT_TYPE_CONST, {.i64=GF_OFFSETTING}, INT_MIN, INT_MAX, FLAGS, "flags" },
         { "transdiff", "enable transparency detection between frames", 0, AV_OPT_TYPE_CONST, {.i64=GF_TRANSDIFF}, INT_MIN, INT_MAX, FLAGS, "flags" },
-    { "gifimage", "enable encoding only images per frame", OFFSET(image), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS, "flags" },
+    { "gifimage", "enable encoding only images per frame", OFFSET(image), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS },
     { NULL }
 };