[BUGFIX] IndexSearch still uses require_once

Remove the old magic as classes are loaded properly already.

Resolves: #58567
Related: #47852
Releases: 6.2
Change-Id: Iec20bf0dbd6955950225936911eba604faf720d6
Reviewed-on: https://review.typo3.org/29898
Reviewed-by: Oliver Klee
Reviewed-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn