build_packages.sh: Remove regencache, eclean pkgs

Remove regen Portage cache and eclean stale binpkgs as it has migrated
to Python.

BUG=b:218521900
TEST=CQ

Cq-Depend: chromium:3582187
Change-Id: I53bfbc424bbb2ece5f574af57ada56dc35cf9dfd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3582405
Tested-by: Cindy Lin <xcl@google.com>
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
Commit-Queue: Cindy Lin <xcl@google.com>
1 file changed