Realign "arc land" closed/published warning around more modern language

Summary: Ref T13546. The modern constant from the modern API method for this state is "published", and this more narrowly covers the desired behavior (notably, excluding "Abandoned" revisions).

Test Plan: Ran "arc land ... --revision X" where "X" is a published revision, got an appropriate prompt.

Maniphest Tasks: T13546

Differential Revision: https://secure.phabricator.com/D21345