[BUGFIX] Remove outdated PHPDoc comment

The described behavior has been removed with TYPO3 7.6;
the variable is treated as a boolean now.

Resolves: #79314
Releases: master
Change-Id: I456ad1884a9a40c22c2015d19aa5abdd623a1654
Reviewed-on: https://review.typo3.org/51308


Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>