Remove confusing recalc flag from simplify update callback

PSYS_RECALC_CHILD is not handled by handle_object_update at
all so it was rather pointless to set this flag.

Double-checked with Brecht.

source/blender/makesrna/intern/rna_scene.c

@@ -1270,8 +1270,6 @@ static void object_simplify_update(Object *ob)
 
 	for (md = ob->modifiers.first; md; md = md->next) {
 		if (ELEM3(md->type, eModifierType_Subsurf, eModifierType_Multires, eModifierType_ParticleSystem)) {
-			/* TODO(sergey): Figure out what da heck we're using PSYS flag on object.  */
-			ob->recalc |= PSYS_RECALC_CHILD;
 			DAG_id_tag_update(&ob->id, OB_RECALC_DATA);
 		}
 	}