[TASK] Merge submodules of EXT:linkvalidator

The two submodules "Check Links" and "Report" of backend module
"Check Links" have been merged into one view. Language keys that are no
longer used have been deleted in the process.

If no page has been selected in the page tree, a corresponding info box
now appears.

Further improvements to this backend module will be made in further
patches.

Resolves: #104145
Releases: main
Change-Id: Ic9331b6e58bf5986bc0e84416276faaec149e575
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84702


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: core-ci <typo3@b13.com>