Add the following to your themes functions.php.

functions.php

<?php
// Copy everything below the line to your themes functions.php file.
// ------------------------------------------------------

add_action( 'after_setup_theme', 'remove_pum_shortcode_ui' );
function remove_pum_shortcode_ui() {
	if ( class_exists( 'PUM_Admin_Shortcode_UI' ) ) {
		remove_action( 'admin_init', array( PUM_Admin_Shortcode_UI::instance(), 'init_editor' ), 20 );
	}
}