[BUGFIX] #5086 Old reference to locallang.php in flexforms

Change-Id: I25048fa2cb84607b7b1831f75551539649b51ae5
Reviewed-on: http://review.typo3.org/32532
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>