[Dual Shade] Always show the date on shade header, never notif icons.

Fix: 396092334
Bug: 397195068
Test: Unit tests still pass.
Test: Manually by opening the notifications shade on both narrow and
 wide screens.
Flag: com.android.systemui.scene_container
Change-Id: I375a5a9fa1de6c07ad6bae588fbde65f9bde3047