Cassandra has long been non-functional, doesn't compile, etc.,
and development on it has halted. Since MariaDB Server 10.5,
the build is disabled by default.
It makes sense to remove it as it's just taking up space.
The TokuDB storage engine has been deprecated by upstream
Percona Server 8.0 in favor of MyRocks and will not be available
in subsequent major upstream releases.
Let us remove it from MariaDB Server as well.
MyRocks is actively maintained, and it can be used instead.
