Use NSSL placeholder with clock migration

The status view height is no longer relevant to determine placement of
NSSL. Use the new placeholder's position instead.

Fixes: 317876688
Test: manual; on keyguard, swipe down with notifications visible to
check for smooth animations between SHADE_LOCKED and KEYGUARD
Flag: ACONFIG com.android.systemui.migrate_clocks_to_blueprint
DEVELOPMEN

Change-Id: Ib8efdc3756b19a51fb12099f80a359bda6c0e0ce