[TASK] Simplify load logic of dbal autoloader in install tool

Moving the execute method from ext:dbal/class.tx_dbal_autoloader.php
to Installer.php obsoletes the dbal file.

Change-Id: I62fbfc3a0f2ccbac3e3e0ab259c735f85983260d
Resolves: #47836
Releases: 6.2
Reviewed-on: https://review.typo3.org/20422
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn