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.