Remove support for Unix Domain Sockets in control channel
The support for UDS in control channel (and rndc) has been an fatal error since BIND 9.18. Properly cleanup the code to remove the remnants of it.
We might want to partially backport the named-checkconf changes to BIND 9.18, so it's also a fatal error in BIND 9.18.
Edited by Ondřej Surý