[TASK] Cleanup BackendUtitlity::displayWarningMessages

As the report tool checks system environment with the use of the hook
witin that function, we can deprecate the function in the BackendUtility
and move the hook to the appropriate extension "aboutmodules".

Resolves: #51434
Releases: 6.2
Change-Id: If39a82680a8797782bcbf620d7a3e59193468a9c
Reviewed-on: https://review.typo3.org/23400
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters