It was already disabled in 1589cf1c but
turns out that as long as the packaging is there, is requires maintenance,
ensuring it still builds, debugging failing tests etc and that takes its
toll and is not worth all the extra work. Having it "only disabled" does
not help, since either we have it and keep it tested and working, or we
don't have it and don't spend time on keeping it working and tested.

In MDEV-19780 there was already a decision to drop TokuDB from MariaDB.

If somebody wants TokuDB, they can use the 10.4 branch.