MDL-76583 core: Update uses of external_* classes

lib/tests/fixtures/test_external_function_throwable.php

@@ -14,6 +14,10 @@
 // You should have received a copy of the GNU General Public License
 // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 
+use core_external\external_api;
+use core_external\external_function_parameters;
+use core_external\external_single_structure;
+
 /**
  * An external function that throws an exception, for tests.
  *
@@ -22,17 +26,6 @@
  * @copyright  2020 Dani Palou
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-
-defined('MOODLE_INTERNAL') || die();
-
-require_once("$CFG->libdir/externallib.php");
-
-/**
- * Create an external function that throws an exception, for tests.
- *
- * @copyright  2020 Dani Palou
- * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- */
 class test_external_function_throwable extends external_api {
 
     /**
@@ -58,7 +51,7 @@ class test_external_function_throwable extends external_api {
     /**
      * Returns description of throw_exception() result value.
      *
-     * @return external_description
+     * @return \core_external\external_description
      */
     public static function throw_exception_returns() {
         return new external_single_structure(array());