MDL-45242 Lib: Replace calls to deprecated functions

In all cases changes have been kept to a minimum while not making
the code completely horrible. For example, there are many instances
where it would probably be better to rewrite a query entirely, but
I have not done that (in order to reduce the risk of changes).

search/classes/engine.php

@@ -150,7 +150,8 @@ abstract class engine {
         global $DB;
 
         if (empty(self::$cachedusers[$userid])) {
-            $fields = get_all_user_name_fields(true);
+            $userfieldsapi = \core\user_fields::for_name();
+            $fields = $userfieldsapi->get_sql('', false, '', '', false)->selects;
             self::$cachedusers[$userid] = $DB->get_record('user', array('id' => $userid), 'id, ' . $fields);
         }
         return self::$cachedusers[$userid];