init: remove "reboot_mode"
init: remove "reboot_mode"

Clean up to prepare removing "reboot_mode" utility.

BUG=chromium-os:11748
TEST=none, simply clean up

Change-Id: Ib447378bdb8fb9605ac6c303ff710bdff932a6b1

R=rspangler@chromium.org

Review URL: http://codereview.chromium.org/6880200

joshfire/chromiumos-platform-init