Rename some documentation/comment references to build_packages

build_packages was renamed to `cros build-packages`.  Update comment
strings and docs referencing it.

BUG=b:287469454
TEST=CQ

Change-Id: I3c2cb3af92b6eecbb8909e6025b3777fb73881d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4621769
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Anuj Jamwal <anujjamwal@google.com>
diff --git a/scripts/cros_generate_sysroot.py b/scripts/cros_generate_sysroot.py
index 37b82ce..aae8ca4 100644
--- a/scripts/cros_generate_sysroot.py
+++ b/scripts/cros_generate_sysroot.py
@@ -4,7 +4,7 @@
 
 """Generates a sysroot tarball for building a specific package.
 
-Meant for use after setup_board and build_packages have been run.
+Meant for use after cros build-packases has been ran.
 """
 
 import os