gio: move resolver utils from gresolver.c to gthreadedresolver.c

Since there is only one resolver implementation now, we can move the
resolver utility functions from gresolver.c into gthreadedresolver.c,
and remove the prototypes from gnetworkingprivate.h.

https://bugzilla.gnome.org/show_bug.cgi?id=623187

gio/gnetworkingprivate.h

@@ -78,40 +78,6 @@
 
 G_BEGIN_DECLS
 
-extern struct addrinfo _g_resolver_addrinfo_hints;
-
-GList *_g_resolver_addresses_from_addrinfo (const char       *hostname,
-					    struct addrinfo  *res,
-					    gint              gai_retval,
-					    GError          **error);
-
-void   _g_resolver_address_to_sockaddr     (GInetAddress            *address,
-					    struct sockaddr_storage *sa,
-					    gsize                   *len);
-char  *_g_resolver_name_from_nameinfo      (GInetAddress     *address,
-					    const gchar      *name,
-					    gint              gni_retval,
-					    GError          **error);
-
-#if defined(G_OS_UNIX)
-gint   _g_resolver_record_type_to_rrtype   (GResolverRecordType record_type);
-
-GList *_g_resolver_records_from_res_query  (const gchar      *rrname,
-					    gint              rrtype,
-					    guchar           *answer,
-					    gint              len,
-					    gint              herr,
-					    GError          **error);
-#elif defined(G_OS_WIN32)
-WORD   _g_resolver_record_type_to_dnstype  (GResolverRecordType record_type);
-
-GList *_g_resolver_records_from_DnsQuery   (const gchar      *rrname,
-					    WORD              dnstype,
-					    DNS_STATUS        status,
-					    DNS_RECORD       *results,
-					    GError          **error);
-#endif
-
 gboolean _g_uri_parse_authority            (const char       *uri,
 					    char            **host,
 					    guint16          *port,