Clean up persistent usb state on boot.

b/31814300 was fixed, but mtp can still stick around in the
persistent config even after flashing. This block of code
will only run once, but will ensure that mtp is not in
the config after the update.

Bug: 31814300
Test: Manual
Change-Id: Icf02be38c9e1f769412ac963ed6afc14e6092bfb