flash_ec: remove unused USB and unprotect options

There is no need for the usb flag, remove it.
There is no need for the unprotect flag, remove it.

BRANCH=none
BUG=chrome-os-partner:22990
TEST=run flash_ec before and after

Change-Id: I201bad7f5be63a90bb8168e21baef2c6fa8d85b4
Signed-off-by: Myles Watson <mylesgw@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/273904
Reviewed-by: Randall Spangler <rspangler@chromium.org>