Fix a bug on Calendar event day views for all day events in certain timezones
Ref T11816. This logic was correct, we just did all the work and then mostly threw away the results. This worked correctly anyway in some timezones.
Instead, actually use $min_date and $max_date.
Test Plan: In "America/Toronto" with server in a more-western timezone, viewed a "Nov 11 - Nov 12" all-day event, saw those dates.
Reviewed By: chad
Maniphest Tasks: T11816
Differential Revision: https://secure.phabricator.com/D16867