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
diff --git a/resolv/res_init.cpp b/resolv/res_init.cpp
index 651fc1b..808f44c 100644
--- a/resolv/res_init.cpp
+++ b/resolv/res_init.cpp
@@ -127,13 +127,11 @@
  * Return 0 if completes successfully, -1 on error
  */
 int res_ninit(res_state statp) {
-    extern int __res_vinit(res_state, int);
-
-    return (__res_vinit(statp, 0));
+    return res_vinit(statp, 0);
 }
 
 /* This function has to be reachable by res_data.c but not publicly. */
-int __res_vinit(res_state statp, int preinit) {
+int res_vinit(res_state statp, int preinit) {
     char *cp, **pp;
     char buf[BUFSIZ];
     int nserv = 0; /* number of nameserver records read from file */