R1:dbd7e3c56de4

Remove unused CalendarColors class

Summary: This class is no longer used after D12850.

Test Plan: `grep`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D13119