Remove older versions of Maxima from the settings list.

settings.php

@@ -70,8 +70,7 @@ $settings->add(new admin_setting_configselect('qtype_stack/platform',
 $settings->add(new admin_setting_configselect('qtype_stack/maximaversion',
         get_string('settingcasmaximaversion', 'qtype_stack'),
         get_string('settingcasmaximaversion_desc', 'qtype_stack'), null,
-                array('5.38.1' => '5.38.1', '5.39.0' => '5.39.0',
-                      '5.40.0' => '5.40.0', '5.41.0' => '5.41.0', '5.42.0' => '5.42.0',
+                array('5.40.0' => '5.40.0', '5.41.0' => '5.41.0', '5.42.0' => '5.42.0',
                       '5.42.1' => '5.42.1', '5.42.2' => '5.42.2',
                       '5.43.0' => '5.43.0', '5.43.1' => '5.43.1', '5.43.2' => '5.43.2',
                       '5.44.0' => '5.44.0', 'default' => 'default')));