Make event lists respect the user preference for time format.

Summary: Ref T8362, Make event lists respect the user preference for time format

Test Plan: Set time format preference to 24-hour format, open Calendar month view, all events should show time tips in 24-hour format.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T8362

Differential Revision: https://secure.phabricator.com/D13290