Remove deprecated password validation rule

[netpok]

In #37650 the password rule was renamed to current_password with the intention of removing the old rule in the next major version. This PR removes it.

The original reasoning behind this was that later password could be used as an alias for the new Password::defaults() while I'm still supporting the idea I'm not sure whether it should be done in the next version or in a later one.

The problem with implementing it right away is that it can pass for the provided password even if it's not valid for developers who does not follow the upgrade guide. By waiting a few minor or even a major version we could prevent security issues because it would simply throw an exception.

If it should be included in this version I'm willing to create a pull request for it.

[driesvints]

Feel free to ignore the failing PHP 8.1 tests for now.

Btw, shouldn't we update the tests to use the current_password rule instead?

[netpok]

The current_password rule already have the same tests at line 749

[Jubeki]

I would support aliasing the new Password::defaults() rule to password in Laravel 9.

What about adding an validation config where you can configure the Password rule?

[driesvints]

@netpok if you rebase with master test should pass now

[netpok]

Rebased it

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@Jubeki what do you mean by adding a validation config?

1. If you mean to support the old or the new behavior I'm against that, developers should just simply migrate.
2. If you mean to configure the default password rule you can already do that by using Password::default, adding a new config option (and file) is out of the scope for this PR.