[9.18] Merge branch '3953-deprecate-delegation-only' into 'main'

These options and zone type were created to address the SiteFinder controversy, in which certain TLD's redirected queries rather than returning NXDOMAIN. since TLD's are now DNSSEC-signed, this is no longer likely to be a problem.

The deprecation message for 'type delegation-only' is issued from the configuration checker rather than the parser. therefore, isccfg_check_namedconf() has been modified to take a 'nodeprecate' parameter to suppress the warning when named-checkconf is used with the command-line option to ignore warnings on deprecated options (-i).

Backport of MR !7712 (merged)

See #3953 (closed)