Drop MbsAPI, if not needed, after 19.0 release

[ChristianTackeGSI]

We deprecated and deactivated MbsAPI for 19.0.

If nobody complains, we should remove it for 19.2.

According to a group meeting on 2021-07-26, CBM was using MbsAPI and might be affected. Putting @fuhlig1 in the loop.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will not be closed.