Revert "Add unit test for WallpaperService.Engine#getRenderingSurfaceControl"

This reverts commit a04567dc.

Reason for revert: the test added in this CL is useless. It tests that a class member field that's initialized as null is null before it's initialized. Tests like these add maintenance costs but no real value and shouldn't be merged.

Change-Id: I38f91af04427acc2ada35f25c454aa36e2f398a3