kernel/vm: Drop VMCacheRef::ref_count.

Nothing touches it at all.

headers/private/kernel/vm/vm_types.h

@@ -107,7 +107,6 @@ typedef phys_addr_t page_num_t;
 
 struct VMCacheRef {
 			VMCache*			cache;
-			int32				ref_count;
 
 								VMCacheRef(VMCache* cache);
 };

src/system/kernel/vm/VMCache.cpp

@@ -599,8 +599,7 @@ vm_cache_acquire_locked_page_cache(vm_page* page, bool dontWait)
 
 VMCacheRef::VMCacheRef(VMCache* cache)
 	:
-	cache(cache),
-	ref_count(1)
+	cache(cache)
 {
 }