[SB][Notif] Don't show `when` in chip if automatic promotion is enabled.

Automatically promoted notification will likely just set their `when`
time to the current time, which would cause the chip to always show
"now". We don't want teamfooders to get that experience because it won't
happen in prod, so just don't show any time if we're automatically
promoting notifications.

Bug: 364653005
Flag: com.android.systemui.status_bar_notification_chips
Flag: com.android.systemui.promote_notifications_automatically
Test: Send notif that's auto promoted -> verify time doesn't show
Change-Id: I5acd88fc244c68240210880681b0bbf43d31309c