Draft: Resolve #3391459 "[Opinions welcome] Remove customizable options"

Closes #3391459

config/install/passwordless.settings.yml

-passwordless_add_css: '1'
-passwordless_show_help: '1'
-passwordless_help_link_text: 'What? No password?'
-passwordless_help_text:
-  value: "This website provides passwordless login, an advanced login system that allows people to register and sign on securely with no need to remember a new password—or, worse, to use an insecure one.\r\n\r\nYour account is kept safe by Drupal’s security mechanisms, and the only password you need to remember is the one to your e-mail account. Every time you need to log in, just enter your e-mail address in the form, then click “Log in.” Within seconds, you’ll receive a link that will allow you to log in directly. This link is single-use (meaning that no one else can use it after you), and expires in twenty-four hours.\r\n\r\nIf you use this website from your own computer, chances are you won’t need to receive this link more than once, unless you log out manually or clear your browser’s cookies. If you log in through a shared computer, always remember to log out when you’re finished. The next time you need to log in, just request a new link."
-passwordless_toggle_sent_page: '0'
-passwordless_sent_title_text: 'Check your e-mail!'
-passwordless_sent_page_text:
-  value: "The login link has been sent to your e-mail address.\r\nYou should receive it shortly."
-langcode: en