Hide bubble dot after flyout init

After the flyout initializes to its collapsed state, hide the
notification dot so that the flyout and dot will seem visually as
one.

Flag: com.android.wm.shell.enable_bubble_bar
Fixes: 376276297
Test: atest BubbleBarFlyoutControllerTest
Change-Id: Ie581ddcd56a26844526f80b2169639c1a7d87500