[!!!][TASK] Remove TypoScript option config.doctypeSwitch

"config.doctypeSwitch" was used to bring TYPO3's Frontend
into "Quirks Mode" when using XHTML, important for Internet Explorer.

Internet Explorer is not supported by Microsoft anymore,
and XHTML is superseded by HTML5.

For this reason, TYPO3 Core should not support such an edge-case
anymore.

Resolves: #97927
Releases: main
Change-Id: Ifa9ad9dd460d1c9690cefcd905be469b6d508574
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75167


Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Frank Nägler <frank.naegler@typo3.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>
Reviewed-by: Frank Nägler <frank.naegler@typo3.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>