FRP: clear FRP when setup complete if not set up

When setup completes and the user has not set up a new secure credential,
clear the FRP credential. Otherwise, if the user factory resets again, we
will ask for a stale credential that they never set up.

Change-Id: I824eb6a9308d9783220f670df19869137a9f3a5f
Fixes: 63016537
Test: Set up FRP credential, factory reset, go through setup without setting up a pin/pattern/password, factory reset again, verify not being asked for frp credential