resolved: remove duplicate handling of "no servers" query result

resolved: remove duplicate handling of "no servers" query result

So far we handled immediate "no server" query results differently from
"no server" results we ran into during operation: the former would cause
the dns_query_go() call to fail with ESRCH, the later would result in
the query completion callback to be called.

Remove the duplicate codepaths, by always going through the completion
callback. This allows us to remove quite a number of lines for handling
the ESRCH.

This commit should not alter behaviour at all.