[piav2] Cleanup CL to prepare for single user-confirmation dialog change

This CL attempts to cleanup the code in PIAV2 to account for nullable
InstallStage returned by InstallRepository

Bug: 319320680
Test: Install an APK manually
Change-Id: Ib09fb91e02978181d5d70f77a63ffde8e0c9f35f
2 files changed