Fix rb_remove() to use node's key for comparison

The origin code was erroneously comparing node->data when searching
for the node to remove, instead of using the node->key. This commit
corrects the comparison to use the node->key, ensuring the proper
removal of nodes.

Author: visitorckw

src/map.c

@@ -221,7 +221,7 @@ static void rb_remove(map_t rb, map_node_t *node)
     pathp = path;
     while (pathp->node) {
         map_cmp_t cmp = pathp->cmp =
-            (rb->comparator)(node->data, pathp->node->data);
+            (rb->comparator)(node->key, pathp->node->key);
         if (cmp == _CMP_LESS) {
             pathp[1].node = rb_node_get_left(pathp->node);
         } else {