dev-install: simplify emerge setup phase

We don't need to create most of these paths, just the basic /tmp one.
This will let us simplify the C++ migration by not having to load the
shell script and pull out random variables.

BUG=chromium:935142
TEST=precq passes

Change-Id: I309a3df95aadf79a3613b3fb13dee989c70396c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/1898446
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
2 files changed