Removes undefined `time_input` from `invite_users_modal.hbs`.
The default input value for the expiration custom time limit is
not set until the "custom" option is selected from the dropdown.
Removes the undefined `csrf_input` from the same template. And
imports `csrf.ts` into `invite.js` to get the csrf token and
add it to the request data, which is the current pattern used
in other `/web/src` modules.