deprecate/remove resolver-nonbackoff-tries, resolver-retry-interval

These options were added to named at the same time as serve-stale support. I suspect they were meant to be used for testing, but they weren't documented as test-only options (or, really, as anything else either - see #1687 (closed)).

They are not, in fact, used in any of the system tests, and I can't think of a reason one would want to modify them in production. I suggest we remove them as of 9.20.