rem: usr: Remove DNSRPS implementation from the open-source version

DNSRPS was the API for a commercial implementation of Response-Policy Zones that was supposedly better. However, it was never open-sourced and has only ever been available from a single vendor. This goes against the principle that the open-source edition of BIND 9 should contain only features that are generally available and universal.

This commit removes the DNSRPS implementation from BIND 9. It may be reinstated in the subscription edition if there's enough interest from customers, but it would have to be rewritten as a plugin (hook) instead of hard-wiring it again in so many places.