[FSD2D] Remove left-over code from proof-of-concept

This code was not meant to be shipped and was disabled by default. It
was accidentally enabled when productionizing the final version of FSD2D.

Bug: 184781934
Test: 1. atest CtsBackupTestCases
      2. atest CtsBackupHostTestCases
      3. Run a D2D transfer and verify system apps are properly restored
Change-Id: I47dbc769a316b17a38b6c21d7a1294d7ff977491