Remove `Guard` Class

[Taufik Nurrohman]

I am fine with the term. It is just that the property names is already unique. In Mecha 3.0.0, function aliases related to the Guard class will becomes real functions.

function abort(string $alert, $exit = true) { … }
function check(string $token, $id = 0) { … }
function kick(string $path = null, int $status = null) { … }
function token($id = 0, $for = '1 minute') { … }