Fix EZP-23752: Strict standards error with Symfony 2.6

> https://jira.ez.no/browse/EZP-23752

Removed custom `isGranted()` method from `eZ\Bundle\EzPublishCoreBundle\Controller`
Merge pull request #1111 from ezsystems/fix_EZP-23752_sf2.6StrictStandards

Fix EZP-23752: Strict standards error with Symfony 2.6