[BUGFIX] ConfigurationUtility loses extension key

The EM's ConfigurationUtility::getCurrentConfiguration() method looks for
the extension key at the wrong place. Rather than using the key
it receives as a parameter, it tries to get it from
$GLOBALS['TYPO3_LOADED_EXT'] where it does not exist.

Releases: 6.0, 6.1
Resolves: #44665
Reviewed-on: https://review.typo3.org/17600
Reviewed-by: Francois Suter
Tested-by: Francois Suter
Change-Id: I45b8577254b21183adeb90cb02a10b40098f6d8c
Reviewed-on: https://review.typo3.org/17601