removed leftovers from old versions of wp-piwik plugin

wp-content/plugins/wp-piwik/README.md

-# WP-Piwik
+# WP-Matomo (former WP-Piwik)
 
-This [WordPress](https://wordpress.org) plugin adds a [Piwik](http://piwik.org) stats site to your blog's dashboard. It's also able to add the Piwik tracking code to your blog.
+This [WordPress](https://wordpress.org) plugin adds a [Matomo](http://matomo.org) stats site to your blog's dashboard. It's also able to add the Matomo tracking code to your blog.
 
 ## How to use this plugin
 
-To use this plugin you will need your own Piwik instance. If you do not already have a Piwik setup, you have two simple options: use either [self-hosted](http://piwik.org/) or [cloud-hosted](http://piwik.org/hosting/).
+To use this plugin you will need your own Matomo instance. If you do not already have a Matomo setup, you have two simple options: use either [self-hosted](http://matomo.org/) or [cloud-hosted](http://matomo.org/hosting/).
 
-This repository was created to develop and maintain WP-Piwik. Please see the WordPress plugin directory if you like to use this plugin: https://wordpress.org/plugins/wp-piwik/
+This repository was created to develop and maintain WP-Matomo (WP-Piwik). Please see the WordPress plugin directory if you like to use this plugin: https://wordpress.org/plugins/wp-piwik/

wp-content/plugins/wp-piwik/cache/.htaccess

-Deny from all

wp-content/plugins/wp-piwik/cache/index.php

-<?php
-	// Nothing to see...
\ No newline at end of file