Fixing top notifications cut off on the lockscreen

The main issue was split_shade_header_height referencing quick_qs_offset_height - I changed that relation for sw720dp-land, I can’t think of any good reason that should be still needed.
Also simplifying getSplitShadeStatusBarHeight - it was assuming that split_shade_header_height would be always referencing quick_qs_offset_height.

Fixes: 216919842
Test: Split shade lockscreen with notificaations - swipe up and see if top notification is clipped weirdly
Change-Id: Iabedab351d88d732f9e4aeebb5ad3bacad35d677