Map and icon tweaks.

Re-adds medical examination wall and chapel mass driver button.
Ensures that the chapel crematorium button does not lose its default icon on icon update.
Fixes #11915. Fixes #11894.

code/game/objects/structures/morgue.dm

@@ -413,6 +413,9 @@
 	req_access = list(access_crematorium)
 	id = 1
 
+/obj/machinery/button/crematorium/update_icon()
+	return
+
 /obj/machinery/button/crematorium/attack_hand(mob/user as mob)
 	if(..())
 		return