[TASK] Remove workaround for PHP bug in validEmail()

In GeneralUtility::validEmail() there's still a workaround for
a PHP crash (bug 52929).
This was fixed with PHP 5.3.4 and as TYPO3 6.2
requires 5.3.7, this workaround can be removed.

Resolves: #51386
Releases: 6.2
Change-Id: I5b32e90fd1a99c1cb2bdc261965114b06b4d4a58
Reviewed-on: https://review.typo3.org/23357
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind