Revert "url: fix treatment of some values as non-empty"

This reverts commit 66877216

.

It was agreed that this change contained too much potential ecosystem
breakage, particularly around the inability to `delete` properties off a
`Url` object. It may be re-introduced for a later release, along with
better work on ecosystem compatibility.

PR-URL: #1602
Reviewed-By: Mikeal Rogers <mikeal.rogers@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Forrest L Norvell <forrest@npmjs.com>
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Isaac Z. Schlueter <i@izs.me>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>