Simplify code around mPreviousViewFocusParameters

This is a follow up CL to our previous CL [1], which introduced
ViewFocusParameterInfo.

This CL mechanically simplifies that CL without changing any
semantics.  There should be no observable behavior change.

 [1]: I0331462624351d17399c733cffa84a132f118ab7
      cb0a7808

Bug: 219819349
Bug: 243778447
Test: presubmit
Change-Id: Iee99cd184503ca8720efb3c43a78cf3ba46f94ad