Remove confused parameters of snapshot controller

- Remove allowSnapshotHome: the caller should decide whether
  to include home before calling it. Now the path of transition
  and animation skip snapshot for home explicitly.
- Remove pixelFormat: currently it is always unknown
  and it can be specified from builder.

Bug: 264551777
Test: TaskSnapshotControllerTest
Change-Id: Ia51e7e9b51579632ca5583327a66f4a418a7bcb8