Revert "[BUGFIX] Do not render HTML in Install Tool's flash message"

Some places intentionally use HTML which needs to be passed though in
raw. Patch needs more work.

This reverts commit 2cead56b.

Releases: master
Reverts: #78308
Related: #73143
Change-Id: Ic319f148791a3823c2b1baccd0670b67a1cb78f8
Reviewed-on: https://review.typo3.org/50256


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>