Remove use of pthread_cancel in asnyc threaded resolving. While there
are system where this works, others might leak to resource leakage
(memory, files, etc.). The popular nsswitch is one example where resolve
code can be dragged in that is not prepared.
The overall promise and mechanism of pthread_cancel() is just too
brittle and the historcal design of getaddrinfo() continues to haunt us.
Fixes#18532
Reported-by: Javier Blazquez
Closes#18540
