Remove unused PHUICalendarMonthView::getMaxDailyEventsForWeek()

Summary: Call to this private function was removed in https://we.phorge.it/rPaee9d88c17e25b924ecd5293691cc6fe38d6c7d9.

Test Plan: Grep the code; run static code analysis.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25788