Limit plugin/theme edits and installations

wp-config.php

<?php
/**
 * remove the ability for users to install or edit themes or plugins,
 * you can use the following definitions to take care of that.
 * The first will disable the editors, but still allow installations
 * and updates of themes/plugins, whereas the second definition will disable all of these functions
 *
 **/
 
define('DISALLOW_FILE_EDIT',true);
define('DISALLOW_FILE_MODS',true);