build_packages: Call the sysroot service instead of the shell script

In scripts/build_packages.py, call sysroot.BuildPackages() and
pass along args.
In service/sysroot.py, update BuildPackages to call the shell
script directly and pass along the special chromite flag so
that there aren't deprecation warnings in the build log. Move
construction of the run_config to the caller (build API).

BUG=b:218519852, b:220197678
TEST=manual (`build_packages ...`), CQ

Change-Id: Ied2ff5193ea4852f855e60ed2448efe18e0086c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3448993
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
Tested-by: Cindy Lin <xcl@google.com>
Commit-Queue: Cindy Lin <xcl@google.com>
diff --git a/api/controller/sysroot.py b/api/controller/sysroot.py
index 04cddc4..765472a 100644
--- a/api/controller/sysroot.py
+++ b/api/controller/sysroot.py
@@ -251,6 +251,9 @@
 
   use_flags = [u.flag for u in input_proto.use_flags]
   build_packages_config = sysroot.BuildPackagesRunConfig(
+      accept_licenses='@CHROMEOS',
+      upgrade_chroot=False,
+      use_any_chrome=False,
       usepkg=not compile_source,
       install_debug_symbols=True,
       packages=packages,