remove and transfer INVISIBLE_OBJECTS to branch

include/obj.h

@@ -94,11 +94,7 @@ struct obj {
 	Bitfield(recharged,3);	/* number of times it's been recharged */
 #define on_ice recharged	/* corpse on ice */
 	Bitfield(lamplit,1);	/* a light-source -- can be lit */
-#ifdef INVISIBLE_OBJECTS
-	Bitfield(oinvis,1);	/* invisible */
-#else
-	Bitfield(oreserved1,1);	
-#endif
+	Bitfield(oreserved1,1);	/* was the placeholder for invisible objects, free for use */
 	Bitfield(greased,1);	/* covered with grease */
 	Bitfield(nomerge,1);	/* set temporarily to prevent merging */
 	Bitfield(was_thrown,1);	/* thrown by hero since last picked up */