Revert "Reduce observers in SystemUI: KeyButtonView"

Temporary revert. We will get back to you, observers.

This reverts commit 855f54384d99242bcc25a0de7cfb6c104035b034

Change-Id: If612ee7ca947f5f00bd42d2d45205f50ba2f979d
Merge "Revert "Reduce observers in SystemUI: KeyButtonView"" into jb-mr1