Take bubble selection from the shell update.

Prior to this change, the bubble bar controller determined which bubble
to select. With this change, the selection is now determined by the
update received from the shell.

Test: Manual. Tested the add overflow and remove bubble flows, add
bubble and remove overflow flows, and add bubble and remove bubble flows
Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 359952121

Change-Id: I8ec01d6976b1e1cd0129071fd1765041eeb10b83