Move remaining namespaces and delete Core\Cache.php

mod/poco.php

@@ -6,12 +6,10 @@
 
 use Friendica\App;
 use Friendica\Content\Text\BBCode;
-use Friendica\Core\Cache;
 use Friendica\Core\Config;
 use Friendica\Core\Logger;
 use Friendica\Core\Protocol;
 use Friendica\Core\Renderer;
-use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\DI;
 use Friendica\Protocol\PortableContact;