Remove divider view when exiting splitscreen

Remove and re add divider view as needed so we do not allocate memory
while split screen is not active. Also release surface reference from
server when we are done with the SurfaceControl so we don't have to rely
on GC to remove the last reference.

Fixes: 150190730
Test: test split screen manually, check for offscreen or onscreen
divider layers in winscope

Change-Id: I1a6a1c1d4346aafeae85aaf61ec4df23722e75ab