build_packages.sh: Remove logic for getting pkgs

The base set of packages will be passed as args from Python so remove
the duplicate logic that builds the list of packages from this script.

BUG=b:218521900
TEST=CQ

Cq-Depend: chromium:3607176
Change-Id: I62d60c017a18b2eed1da6c542acc755a400e36b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3607452
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
Commit-Queue: Cindy Lin <xcl@google.com>
Tested-by: Cindy Lin <xcl@google.com>
1 file changed