Use rb_ary_unshare for shared array in rb_ary_replace

rb_ary_unshare will perform FL_UNSET_SHARED and
rb_ary_decrement_share.

array.c

@@ -4392,20 +4392,14 @@ rb_ary_replace(VALUE copy, VALUE orig)
     if (copy == orig) return copy;
 
     if (RARRAY_LEN(orig) <= RARRAY_EMBED_LEN_MAX) {
-        VALUE shared_root = 0;
-
         if (ARY_OWNS_HEAP_P(copy)) {
             ary_heap_free(copy);
 	}
         else if (ARY_SHARED_P(copy)) {
-            shared_root = ARY_SHARED_ROOT(copy);
-            FL_UNSET_SHARED(copy);
+            rb_ary_unshare(copy);
         }
         FL_SET_EMBED(copy);
         ary_memcpy(copy, 0, RARRAY_LEN(orig), RARRAY_CONST_PTR_TRANSIENT(orig));
-        if (shared_root) {
-            rb_ary_decrement_share(shared_root);
-        }
         ARY_SET_LEN(copy, RARRAY_LEN(orig));
     }
     else {