revert 84115 "compatibility TYPO3 6.2"
It was asumed that the new Package Manager did not set the $_EXTKEY, but this was not 
the case. Instead the global $_EXTKEY overwrote the current variable.

git-svn-id: https://svn.typo3.org/TYPO3v4/Extensions/lowlevel_scheduler_task/trunk@84121 735d13b6-9817-0410-8766-e36946ffe9aa