Cleanup: avoid incrementing/decrementing id->us outside of BKE_library.

We have callbacks for that, they also do some checks and help ensure things are done
correctly. Only place where this is assumed not true is blenloader (since here we
may affect refcount of library IDs as well...).

source/blender/blenkernel/intern/sequencer.c

@@ -198,7 +198,7 @@ static void BKE_sequence_free_ex(Scene *scene, Sequence *seq, const bool do_cach
 	}
 
 	if (seq->sound) {
-		((ID *)seq->sound)->us--; 
+		id_us_min(((ID *)seq->sound));
 	}
 
 	if (seq->stereo3d_format) {