The debian/salsa-ci.yml used to work also on upstream MariaDB.org branches,
but has recently regressed and several jobs stopped working. These fixes
are necessary to get it working again.

* Partially revert 8642f592 that never worked, as MariaDB 10.2 does not
  have a mysql.global table nor a mariadb.sys user. Those features weren't
  introduced until MariaDB 10.4.

* Partially revert 0268b871 as we don't want ColumnStore as part of the
  native Debian build. It should build only when the build is triggered
  via autobake-deb.sh (MariaDB.org builds).

* Adjust salsa-ci.yml to cope with various Stretch to Sid upgrade issues
  and remove the legacy mariadb-connector-c job completely as that package
  hasn't been around for years anymore.

* Extend Lintian overrides to be otherwise Lintian clean