merge sdk & board distdirs

We've merged these two dirs to avoid double fetching, so add some
hooks to clean up the old paths as they can take up many GB of data.

BUG=None
TEST=CQ passes

Cq-Depend: chromium:2277139
Change-Id: I3285b9de3373d7bf222c638de8b8e8de742b5c3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2276308
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
3 files changed