[9.x] Allow removing token during tests

[tontonsb]

Once you use a token, you are stuck with an Authorization header for the remainder of the test:

$this->getJson('a');

$this->withToken($token)->getJson('b');

$this->getJson('c'); // also uses the token

This PR adds a small helpers to turn off the token:

$this->getJson('a');

$this->withToken($token)->getJson('b');
$this->getJson('c'); // also uses the token

$this->withoutToken()->getJson('d'); // does not use the token
$this->getJson('e'); // no token either