[VRR] Windowless Snapshot shouldn't vote for frame rate

Fixes: 343755505

The Windowless Snapshot surface doesn't need to use the View
system's voting mechanism. Instead, it should fall back on
SurfaceFlinger's frame rate calculator so that visible Activities
aren't pushed to 120Hz unnecessarily.

Test: manual
Change-Id: I4195549d93818ffb9187401b6f96cff04261ade1