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).

admin/tool/dataprivacy/classes/api.php

@@ -189,7 +189,8 @@ class api {
         $dpos = [];
         $context = context_system::instance();
         foreach ($dporoles as $roleid) {
-            $allnames = get_all_user_name_fields(true, 'u');
+            $userfieldsapi = \core\user_fields::for_name();
+            $allnames = $userfieldsapi->get_sql('u', false, '', '', false)->selects;
             $fields = 'u.id, u.confirmed, u.username, '. $allnames . ', ' .
                       'u.maildisplay, u.mailformat, u.maildigest, u.email, u.emailstop, u.city, '.
                       'u.country, u.picture, u.idnumber, u.department, u.institution, '.