[BUGFIX] Properly discard workspace MM relations

A first patch towards more reliable workspace-mm scenarios:
When a record is discarded that has mm relations, those
relations are now deleted along with the deleted "parent"
record.

Change-Id: Ic2abe8d1c828158cf86abe760aec8766abcd0e71
Resolves: #93064
Releases: master, 10.4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/67100


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>