[TASK] Remove compat layer for about module

Patch deletes compat layer for class CustomSectionsInterface as it's newly
introduced in TYPO3 6.0

Change-Id: I22b9ffa117099d0ca86b0e8fb50a8d52c6182b8b
Resolves: #40360
Related: #40095
Related: #40240
Releases: 6.0
Reviewed-on: http://review.typo3.org/14173
Reviewed-by: Thomas Maroschik
Tested-by: Thomas Maroschik

typo3/sysext/about/ext_autoload.php

-<?php
-$extensionPath = \TYPO3\CMS\Core\Extension\ExtensionManager::extPath('about');
-return array(
-	'tx_about_customsections' => $extensionPath . '/interfaces/interface.tx_about_customsections.php'
-);
-?>
\ No newline at end of file

typo3/sysext/about/interfaces/interface.tx_about_customsections.php

-<?php
-/*
- * @deprecated since 6.0, the classname tx_about_customSections and this file is obsolete
- * and will be removed by 7.0. The class was renamed and is now located at:
- * typo3/sysext/about/Classes/CustomSectionsInterface.php
- */
-require_once \TYPO3\CMS\Core\Extension\ExtensionManager::extPath('about') . 'Classes/CustomSectionsInterface.php';
-?>
\ No newline at end of file