Use $custom_layer_key as $layer_switcher_key.

Closes #3257598

leaflet_more_maps.module

@@ -587,7 +587,7 @@ function _leaflet_more_maps_assemble_custom_map_info(string $custom_map_key, arr
       // Unique.
       $custom_layer_key = "$map_key $layer_key";
       if (in_array($custom_layer_key, $selected_layer_keys)) {
-        $layer_switcher_key = t('layer') . " #$i";
+        $layer_switcher_key = $custom_layer_key;
         $map_info["~$custom_map_key"]['layers'][$layer_switcher_key] = $layer;
         $i = $reverse_order ? $i - 1 : $i + 1;
       }