url: remove invalid file protocol check

'file' should have been 'file:' but since the WHATWG URL spec
suggests using an opaque origin (which is what was already being
used for file URLs), we'll just keep using that, making this merely
a cleanup.

PR-URL: https://github.com/nodejs/node/pull/11691


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>