[!!!][TASK] Remove legacy entrypoint for Install Tool

The entrypoint located under "typo3/sysext/install/Start/Install.php" has been
removed, as the entrypoint "typo3/install.php" is the new way to access the install
tool. The legacy entrypoint "typo3/install/index.php" will still be kept, as it is
easy for existing users to get a simple redirect (still marked as deprecated).

Resolves: #82433
Releases: master
Change-Id: I36a165649c7ca5a988379b70328e570fc45285b0
Reviewed-on: https://review.typo3.org/54093


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>