1) Clean up BiometricDialogImpl. As a side-effect of 2, which cleans up
the dialog lifecycle, we no longer need to have a handler here. This
greatly simplifies the code here.
2) Clean up interface between BiometricDialogImpl and the UI
(BiometricDialogView).
3) Clean up interface between BimetricService and BiometricDialogImpl.
SystemUI is now responsible for dismissing the dialog.
Test: atest BiometricDialogImplTest
Bug: 138628043
Change-Id: Ic1fea4c05c27dfc7eb6fc661f517f0380b9fff99
c53d981e24