MDL-84000 reportbuilder: move testcase helper to autoloaded namespace.

Clean up some class imports while we're at it.

notes/tests/reportbuilder/datasource/notes_test.php

@@ -20,13 +20,8 @@ namespace core_notes\reportbuilder\datasource;
 
 use core_notes_generator;
 use core_reportbuilder_generator;
-use core_reportbuilder_testcase;
 use core_reportbuilder\local\filters\{date, select, text};
-
-defined('MOODLE_INTERNAL') || die();
-
-global $CFG;
-require_once("{$CFG->dirroot}/reportbuilder/tests/helpers.php");
+use core_reportbuilder\tests\core_reportbuilder_testcase;
 
 /**
  * Unit tests for notes datasource