[BUGFIX] Remove outdated information about doktype 5 from tsref.xml

Once upon a time there was a doktype 5 for "not in menu" pages which has
been moved to a checkbox since a long time.

The outdated information can be removed.

Resolves: #90472
Releases: master
Change-Id: I8755a69cad778afe25527e90521963b5cb87de68
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63441


Tested-by: Christian Eßl <indy.essl@gmail.com>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Eßl <indy.essl@gmail.com>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Benni Mack <benni@typo3.org>