Revert "parallel_emerge: Work around Portage library bug with usepkg"

This reverts commit 14e53987cfbb1e99fa72f7517910acbb4e8ca5d4.
The revert is required to fix sdk builder breakage.

BUG=chromium:757824, chromium:757147
TEST=Chromiumos-sdk builder works after reverting the CL.
TEST=https://uberchromegw.corp.google.com/i/chromiumos.tryserver/builders/chromiumos-sdk/builds/2504

Change-Id: Ifa65f82f9b39b27eb56b8152adf14103202a2b5f
Reviewed-on: https://chromium-review.googlesource.com/625377
Trybot-Ready: Brian Norris <briannorris@chromium.org>
Tested-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Jason Clinton <jclinton@chromium.org>
Commit-Queue: Jason Clinton <jclinton@chromium.org>
1 file changed