rm obsolete include.

this came up while adding test coverage. see MDL-76583.
without the include, we can also get rid of the direct script access check.

classes/external/monitor.php

@@ -24,10 +24,6 @@
 
 namespace tool_externaltaskmonitor\external;
 
-defined('MOODLE_INTERNAL') || die();
-
-require_once($CFG->dirroot . '/lib/externallib.php');
-
 use context_system;
 use core\task\manager;
 use dml_exception;