Remove unused use statements & remove PConfig class

src/Core/PConfig.php

@@ -1,22 +0,0 @@
-<?php
-/**
- * User Configuration Class
- *
- * @file include/Core/PConfig.php
- *
- * @brief Contains the class with methods for user configuration
- */
-namespace Friendica\Core;
-
-use Friendica\DI;
-
-/**
- * @brief Management of user configuration storage
- * Note:
- * Please do not store booleans - convert to 0/1 integer values
- * The DI::pConfig()->get() functions return boolean false for keys that are unset,
- * and this could lead to subtle bugs.
- */
-class PConfig
-{
-}