Remove documentation for rndc keydone

This feature never made it through the 9.9 development cycle; it is
now covered by `rndc signing` which is adequately documented
elsewhere.

doc/design/keydone

@@ -1,41 +0,0 @@
-<!--
-Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-
-SPDX-License-Identifier: MPL-2.0
-
-This Source Code Form is subject to the terms of the Mozilla Public
-License, v. 2.0.  If a copy of the MPL was not distributed with this
-file, you can obtain one at https://mozilla.org/MPL/2.0/.
-
-See the COPYRIGHT file distributed with this work for additional
-information regarding copyright ownership.
--->
-
-        rndc keydone <rdata> zone [class [view]]
-
-        e.g.
-                rndc keydone 0549E00001 example
-
-        Last 4 characters need to be 0001 (00=no flags, 01=done)
-        First 2 characters (algorithm) not 00 (algorithm 0 which
-        is reserved, 00 => NSEC3PARAMETERS are encoded in the record)
-        All hexadecimal case insensitive.  length 10.
-                Err: DNS_R_SYNTAX
-
-        The control code will select the zone based on 'zone [class
-        [view]]'.
-                Err: DNS_R_NOTFOUND
-
-        zone must be a primary (signed inline == primary) or normal
-        dynamic zone.
-                Err: DNS_R_NOTPRIMARY
-
-        dns_zone_<something>(zone, text) which will send a event
-        to the zone so that the deletion gets run in the zone's
-        task.  The event handler will delete the record, update the
-        SOA and write out the journal.
-                Err: ISC_R_NOMEMORY
-
-        'zone' can refer to a normal dynamic master zone or a inline
-        zone.
-