[TASK] Indexed Search: remove `milliseconds()` helper method

This patch removes the static `IndexedSearchUtility::milliseconds()`
method, which is used a few times only.

Resolves: #102923
Releases: main
Change-Id: Icfb8cc1bd01c913f9683310c4bc601100ff1e4d8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82643


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>