install_toolchain: remove old hack

BUG=None
TEST=trybot run on chromiumos-sdk

Change-Id: Ie6708f814d6520c901f942a04bdb918746529982
Reviewed-on: https://chromium-review.googlesource.com/260960
Trybot-Ready: Bertrand Simonnet <bsimonnet@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
1 file changed