keygeneration: drop board name from UEFI key generation scripts

Follow up the code review comments on CL:995174, which was merged as
7dff0105d66fa597741604cf1652a72c7a8463ac
("keygeneration: add support for UEFI key generation")

BUG=b:62189155
TEST=See the following commit.
BRANCH=none

Change-Id: Id642029010e4eea51ec1f7d23240678f3f07e872
Reviewed-on: https://chromium-review.googlesource.com/1024917
Commit-Ready: Edward Jee <edjee@google.com>
Tested-by: Edward Jee <edjee@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
7 files changed