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).

lib/classes/task/send_failed_login_notifications_task.php

@@ -115,7 +115,8 @@ class send_failed_login_notifications_task extends scheduled_task {
 
         // Now, select all the login error logged records belonging to the ips and infos
         // since lastnotifyfailure, that we have stored in the cache_flags table.
-        $namefields = get_all_user_name_fields(true, 'u');
+        $userfieldsapi = \core\user_fields::for_name();
+        $namefields = $userfieldsapi->get_sql('u', false, '', '', false)->selects;
         $sql = "SELECT * FROM (
                         SELECT l.*, u.username, $namefields
                           FROM {" . $logtable . "} l

lib/classes/task/send_new_user_passwords_task.php

@@ -47,7 +47,8 @@ class send_new_user_passwords_task extends scheduled_task {
         // Generate new password emails for users - ppl expect these generated asap.
         if ($DB->count_records('user_preferences', array('name' => 'create_password', 'value' => '1'))) {
             mtrace('Creating passwords for new users...');
-            $usernamefields = get_all_user_name_fields(true, 'u');
+            $userfieldsapi = \core\user_fields::for_name();
+            $usernamefields = $userfieldsapi->get_sql('u', false, '', '', false)->selects;
             $newusers = $DB->get_recordset_sql("SELECT u.id as id, u.email, u.auth, u.deleted,
                                                      u.suspended, u.emailstop, u.mnethostid, u.mailformat,
                                                      $usernamefields, u.username, u.lang,