These two pages should not be crawled and stored by search engines.
They are only relevant once, when the user registers and they shouldnt be cached by search engines as it is useless and affects SEO, having the same page contents thousands of times from every installed phpbb forum.

I hard about using the nofollow attribute in phpbb in the future, so these pages should make use of it.

https://www.phpbb.com/community/ucp.php?mode=privacy
https://www.phpbb.com/community/ucp.php?mode=terms
https://www.phpbb.com/community/search.php
https://www.phpbb.com/community/faq.php