[TASK] Move check if workspaces extension is loaded to the controller

Instead of using a ViewHelper the logic can be moved to the controller
where it belongs.

As the ViewHelper is not a public API it can be dropped without a
RST file.

Resolves: #83900
Releases: master
Change-Id: I8d089761b8a168f00cb0739742fa658d40687379
Reviewed-on: https://review.typo3.org/55719


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>