remove and transfer INVISIBLE_OBJECTS to branch

src/mon.c

@@ -303,11 +303,6 @@ unsigned corpseflags;
 	 */
 	if (Blind && !sensemon(mtmp)) obj->dknown = 0;
 
-#ifdef INVISIBLE_OBJECTS
-	/* Invisible monster ==> invisible corpse */
-	obj->oinvis = mtmp->minvis;
-#endif
-
 	stackobj(obj);
 	newsym(x, y);
 	return obj;
@@ -858,9 +853,6 @@ mpickstuff(mtmp, str)
 		if (!touch_artifact(otmp,mtmp)) continue;
 		if (!can_carry(mtmp,otmp)) continue;
 		if (is_pool(mtmp->mx,mtmp->my)) continue;
-#ifdef INVISIBLE_OBJECTS
-		if (otmp->oinvis && !perceives(mtmp->data)) continue;
-#endif
 		if (cansee(mtmp->mx,mtmp->my) && flags.verbose)
 			pline("%s picks up %s.", Monnam(mtmp),
 			      (distu(mtmp->mx, mtmp->my) <= 5) ?