[BUGFIX] Invalid XLIFF attribute xml:space="preserver"

XLIFF does not validate since xml:space must be
either "default" or "preserve".
This attribute is dropped altogether since it is useless.

Change-Id: I075eabfd95359aa4d00ca5b1655399211648042d
Resolves: #67813
Releases: master
Reviewed-on: http://review.typo3.org/40723


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>