sepolicy: add vendor prefix to usb properties

Define property context for vendor.usb.* and allow access to
the same for vendor_init and qti_init_shell. Also remove the
definitions of sys_usb_configfs and sys_usb_controller since
they are redefinitions of the same properties already part of
exported_system_radio_prop and exported2_system_prop and are
already granted to vendor_init and recovery (via coredomain).

Change-Id: Ia394934cb9f34032b95701f768d9ed4e26819ac5