Restore StatusBarStatePolicy.

The StatusBarStatePolicy used to be injected into StatusBar but never
used. It turns out it registered listeners during its construction,
so there were side-effects to this.

Move those registrations into their own #init method and call it
excplitly in StatusBar.

Fixes: 203527754
Test: manual
Change-Id: Iaacd3f03c57d3943be8f362d3252395c3dfaba5c