Revert "Bug 988079 - [Calendar] day view sometimes adds duplicated days to the DOM"

This reverts commit 277ef605c8f8305fe91a65559bfe35ca3458852b.

Conflicts:
	apps/calendar/test/marionette/day_view_test.js
	apps/calendar/test/unit/views/day_test.js
Bug 989785 - apps/calendar/test/marionette/week_view_test.js failing because of week view regression
Merge pull request #17831 from millermedeiros/989785-backout-duplicated-dom

Bug 989785 - apps/calendar/test/marionette/week_view_test.js failing because of week view regression r=gaye