Curl_resolver_is_resolved: show proper host name on failed resolve
resolver_error: remove wrong error message output

The attempt to use gai_strerror() or alternative function didn't work as
the 'sock_error' field didn't contain the proper error code. But since
this hasn't been reported and thus isn't really a big deal I decided to
just scrap the whole attempt to output the detailed resolver error and
instead remain with just stating that the resolving of the name failed.