Several bug fixes for timer notification.

A buzzing timer notification wasn't getting removed when the timer was deleted, or when +1minute was hit.
Timer notification was overlapping with stopwatch notification.
Ongoing timer notification didn't disappear immediately when a timer went off.
Small typo in timer notification.

Bug: 7282162
Bug: 7274564
Change-Id: I3e9f992f23c0739ed356f738b182ea3d09590524