MDL-76583 core: Update uses of external_* classes

lib/adminlib.php

@@ -205,11 +205,10 @@ function uninstall_plugin($type, $name) {
     }
     $plugininfo = null;
 
-    // perform clean-up task common for all the plugin/subplugin types
+    // Perform clean-up task common for all the plugin/subplugin types.
 
-    //delete the web service functions and pre-built services
-    require_once($CFG->dirroot.'/lib/externallib.php');
-    external_delete_descriptions($component);
+    // Delete the web service functions and pre-built services.
+    \core_external\util::delete_service_descriptions($component);
 
     // delete calendar events
     $DB->delete_records('event', array('modulename' => $pluginname));