Update USB tests for ADB split

The AdbService handles all the ADB keys and toggling, so remove the
calls to it from the UsbTests which won't necessarily run on devices
that only have ADB but no USB ports.

Test: cts-tradefed run cts -m CtsUsbTests
Change-Id: I3242d4d2f80e71a744fc52645daffb8344717d4d