[TASK] gitlab-ci: Drop notify stage

gerrit voting and slack nightly reporting is now done
with a gitlab webhook instead of a CI stage.

Change-Id: I6498c41229cb3b6a9178d2a91dbbfbb657034cce
Resolves: #94035
Releases: master, 10.4, 9.5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68956


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>