rem: usr: Move contributed DLZ modules into a separate repository
The DLZ modules are poorly maintained as we only ensure they can still be compiled, the DLZ interface is blocking, so anything that blocks the query to the database blocks the whole server and they should not be used except in testing. The DLZ interface itself is going to be scheduled for removal.
The DLZ modules now live in https://gitlab.isc.org/isc-projects/dlz-modules repository.
Closes #4865
Edited by Ondřej Surý