[TASK] Merge extra_page_cm_options into backend

Move the lines of the hook of extra_page_cm_options into EXT:backend
to cleanup up the core.

Resolves: #55136
Releases: 6.3
Change-Id: I318888775f4ec02caec6b0cb35f1e461f748224d
Reviewed-on: http://review.typo3.org/32665
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>