build_packages.sh: Remove migrated USE flags

Exporting USE flags as environment variables has been migrated to Python
so remove the duplicated logic from this script.

BUG=b:218521368
TEST=CQ

Cq-Depend: chromium:3570401
Change-Id: I72e9e241a93c915e5f45d39048de90fb9aa600ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3570044
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
Tested-by: Cindy Lin <xcl@google.com>
Commit-Queue: Cindy Lin <xcl@google.com>
1 file changed