drop get_default_board usage

The common code will set up DEFAULT_BOARD for us automatically now.

BUG=None
TEST=`cbuildbot {arm,amd64,x86}-generic-full` works

Change-Id: I28e1e05202480c4b158da0e90bcc654ea9cd1cdb
Reviewed-on: https://gerrit.chromium.org/gerrit/30752
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
3 files changed