update_chroot: clean out old binpkgs

Once we've finished updating, clear out all the old binpkgs.  We do this
for boards already in build_image, but we kind of forgot about the sdk.

BUG=None
TEST=`./update_chroot` finished with nuking lots of stale binpkgs

Change-Id: Ic7e4bd728e940248f2dae4dc7490406f6112947a
Reviewed-on: https://chromium-review.googlesource.com/728182
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed