url: mark ignored return value in node::url::Parse(...)

This is to resolve an unused result warning in node_url.cc.
Resolve macro redefinition warning on Windows

PR-URL: https://github.com/nodejs/node/pull/10141


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>