SKIP cache flush ordering on NTA expiry

SKIP cache flush ordering on NTA expiry

dns_view_flushnode() was called in the delete_expired() async
callback, which runs after the query that detected the NTA expiry.
This created a race: the query would proceed with stale cached data
from the NTA period before the flush had a chance to run, resulting
in transient SERVFAIL with EDE 22 (No Reachable Authority).

Skip dns_view_flushnode() in the older branches as the solutions for
older branches are too complicated and this was not a critical bug.

(cherry picked from commit da8e1c956a9ae9134b2df511f0eba8efcceb77c7)