Prevent start usbd twice during booting

During init process, UsbGadget would setprop to
vendor.usb.config while it is null and
persist.vendor.usb.usbradio.config has value.
This action would cause starting usbd twice actually,
one from persist.vendor.usb.usbradio.config and another
from vendor.usb.config. Remove the persist prop action
to prevent this issue.

Bug: 146810930
Test: it only starts usbd once
Change-Id: I18a767fa21cd0fde09a49276f6bd01b257e4aa9e
Signed-off-by: Puma Hsu <pumahsu@google.com>