resolv: dead code removal

 - hostalias() and res_hostalias(): these were no-ops

 - res_opt(), res_querydomain(), p_option(), p_query(),
   res_isourserver(), res_nisourserver(): had no callers

 - res_ourserver_p(): made local to res_data.cpp

 - res_send_setqhook(): unused, DnsProxyListener sets the qhook directly
   in android_net_context, which is then copied to res_state by
   res_setnetcontext(). We can further simplify it later on.

Test: atest netd_integration_test
Change-Id: I70f72202e5b940986cac67dc99ab9461af882187