Get rid of /usr/share/dict/words file

The file is used for password generation but is not present on every system and therefore partially breaks platform independence. Currently, it also slows down CI jobs quite a bit.

• Reviewers can specify who is tutor by sending passwords per email
• Students do not have passwords. See #31 (closed).

There should be no need for this afterwards or we just use xkcdpass with reasonably long passwords of just random garbage passwords.