MDL-80544 core_h5p: Remove the h5plib_v124 plugin

The h5plib_v124 plugin can be removed because it has been replaced
with h5plib_v126, which is using the latest versions of the
libraries.

lib/classes/plugin_manager.php

@@ -1728,6 +1728,7 @@ class core_plugin_manager {
             'editor' => array('tinymce'),
             'enrol' => array('authorize'),
             'filter' => array('censor'),
+            'h5plib' => array('v124'),
             'media' => array('swf'),
             'portfolio' => array('picasa', 'boxnet'),
             'qformat' => array('webct'),