test: disable node subnet replacement tests

### Summary

- Disabled tests related to node replacement in subnet.

### Details

- Marked `should_add_node_and_replace_existing_node_in_subnet` as ignored in `do_add_node.rs` pending Consensus team support.
- Marked `should_replace_node_in_subnet_and_update_allowance` as ignored in `do_remove_node_directly.rs` pending Consensus team support.

### Additional Changes

- Introduced `replacements_of_nodes_in_subnets_enabled` flag set to `false` in `do_remove_node_directly.rs` to conditionally control node replacement logic.

rs/registry/canister/src/mutations/node_management/do_add_node.rs

@@ -769,6 +769,8 @@ mod tests {
         assert!(e.contains("do_add_node: There is already another node with the same IPv4 address"));
     }
 
+    // This test is disabled until the Consensus team is ready to support direct replacement of nodes that are active in a subnet.
+    #[ignore]
     #[test]
     fn should_add_node_and_replace_existing_node_in_subnet() {
         // This test verifies that adding a new node replaces an existing node in a subnet

rs/registry/canister/src/mutations/node_management/do_remove_node_directly.rs

@@ -149,8 +149,10 @@ impl Registry {
         // 4. Check if node is in a subnet, and if so, replace it in the subnet by updating the membership in the subnet record.
         let subnet_list_record = get_subnet_list_record(self);
         let is_node_in_subnet = find_subnet_for_node(self, payload.node_id, &subnet_list_record);
+        // Disabled until the Consensus team is ready to support direct replacement of nodes that are active in a subnet.
+        let replacements_of_nodes_in_subnets_enabled = false;
         if let Some(subnet_id) = is_node_in_subnet {
-            if new_node_id.is_some() {
+            if new_node_id.is_some() && replacements_of_nodes_in_subnets_enabled {
                 // The node is in a subnet and is being replaced with a new node.
                 // Update the subnet record with the new node membership.
                 let mut subnet_record = self.get_subnet_or_panic(subnet_id);
@@ -626,6 +628,8 @@ mod tests {
         registry.do_remove_node(payload, node_operator_id);
     }
 
+    // This test is disabled until the Consensus team is ready to support direct replacement of nodes that are active in a subnet.
+    #[ignore]
     #[test]
     fn should_replace_node_in_subnet_and_update_allowance() {
         let mut registry = invariant_compliant_registry(0);