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/lp/classes/external.php

@@ -879,8 +879,9 @@ class external extends external_api {
             $USER->id, SQL_PARAMS_NAMED);
 
         // TODO Does not support custom user profile fields (MDL-70456).
-        $extrasearchfields = \core\user_fields::get_identity_fields($context, false);
-        $fields = \user_picture::fields('u', $extrasearchfields);
+        $userfieldsapi = \core\user_fields::for_identity($context, false)->with_userpic();
+        $fields = $userfieldsapi->get_sql('u', false, '', '', false)->selects;
+        $extrasearchfields = $userfieldsapi->get_required_fields([\core\user_fields::PURPOSE_IDENTITY]);
 
         list($wheresql, $whereparams) = users_search_sql($query, 'u', true, $extrasearchfields);
         list($sortsql, $sortparams) = users_order_by_sql('u', $query, $context);