cros_bundle_firmware: reduce number of file copies

There's now an input file and an output file. No partial copies at
various points in time that are never again looked at and no multiple
names for what is essentially the same thing.

BUG=chromium:595715
BRANCH=none
TEST=bit-identical result

Change-Id: Ic2a9508351fbfb564f001a8b689a6da174fe6cb1
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://chromium-review.googlesource.com/418776
Commit-Ready: Patrick Georgi <pgeorgi@chromium.org>
Tested-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
2 files changed