[!!!][TASK] Remove workaround to make f:format.html work in BE context

Remove hacky workaround of loading TSFE into the BE context. An
exception is now thrown, if this ViewHelper is invoked in BE context.
Since TYPO3 v11 there are many alternatives: f:sanitize.html,
f:transform.html or even f:format.raw.

Resolves: #101084
Related: #99031
Related: #100963
Releases: main
Change-Id: I873fc75f1293cbffdc32666807d777e3dadf5ddf
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79401


Tested-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>