Fix renderengine_test to work with new async drawLayers API

Removed one test that no longer applies due to changes to the
drawLayers API that no longer takes a fence as an optional input
param.

Also cleaned up other tests to make better use of the fence now
returned by drawLayers.

Bug: 180657548
Test: atest librenderengine_test
Change-Id: I4f270ab8f921ea1ffde1a38fcdbec90cbfc3390a