[TASK] Remove useCrawlerForExternalFiles setting from Indexed Search

This removes an obsolete configuration from the Indexed Search.
It was earlier used to use the TYPO3 Crawler for indexing
external files. As the TYPO3 Crawler isn't used anymore
as a direct dependency of Indexed Search this can be removed.

Resolves: #98945
Releases: main
Change-Id: I5717e4fc6c081aeb023359ea8b76a3ecaa3b5100
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76320


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Benni Mack <benni@typo3.org>