Don't include usb.core in btchipPersoWizard.py
Don't include usb.core in btchipPersoWizard.py

It's useless and it enforce pyusb to be a mandatory depends, but on not-Windows it's not needed.
LedgerHQ/btchip-python,LedgerHQ/btchip-python,LedgerHQ/btchip-python