Remove unneeded cast

`start` is of type uintptr_t so it does not need to be casted to VALUE.

gc.c

@@ -2099,7 +2099,7 @@ heap_page_allocate(rb_objspace_t *objspace, rb_size_pool_t *size_pool)
     /* adjust obj_limit (object number available in this page) */
     start = (uintptr_t)((VALUE)page_body + sizeof(struct heap_page_header));
 
-    if ((VALUE)start % BASE_SLOT_SIZE != 0) {
+    if (start % BASE_SLOT_SIZE != 0) {
         int delta = BASE_SLOT_SIZE - (start % BASE_SLOT_SIZE);
         start = start + delta;
         GC_ASSERT(NUM_IN_PAGE(start) == 0 || NUM_IN_PAGE(start) == 1);