[BUGFIX] Doctype set to html5 should not render xmlns attribute

If the doctype is explicitly set to html5, the attribute xmlns
should still not be rendered.

Resolves: #70300
Releases: master
Change-Id: I61abc836926213c24a9fe04e3df50d3baf9d4a9c
Reviewed-on: http://review.typo3.org/43875


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>