[TASK] Cleanup code in EXT:linkvalidator/Task

Change-Id: Iacb2096a06e7610213e0e40eabf3e2b71e810dac
Resolves: #76670
Releases: master
Reviewed-on: https://review.typo3.org/48595


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>