build_packages: Drop special logic for chromeos-config

chromeos-config now no longer uses virtual packages for the bsp
packages, meaning:

- No special logic is required anymore for force rebuilding the
  package -- the subslot dependency on the bsp packages will rebuild
  if necessary.
- We can drop the chromeos-config from the grep in revdep calculation,
  since the dependencies are now fully proper.

BUG=b:197038156
TEST=build_packages --board strongbad

Change-Id: If53b2cafec205c203647b573072c95ce0c87994d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3166798
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Chris McDonald <cjmcdonald@chromium.org>
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Auto-Submit: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
diff --git a/build_packages b/build_packages
index 115d567..a781f3a 100755
--- a/build_packages
+++ b/build_packages
@@ -267,9 +267,7 @@
 
 # Figure out which packages we should be building.
 PACKAGES=( "$@" )
-# Force rebuild chromeos-config because it is extremely cheap, and we do not
-# want to reuse stale configs.
-FORCE_LOCAL_BUILD_PKGS=( chromeos-base/chromeos-config )
+FORCE_LOCAL_BUILD_PKGS=()
 if [[ $# -eq 0 ]]; then
   PACKAGES=( virtual/target-os )
   if [[ "${FLAGS_withdev}" -eq "${FLAGS_TRUE}" ]]; then
@@ -403,7 +401,7 @@
     sudo -E "${EMERGE_CMD[@]}" "${SIM_EMERGE_FLAGS[@]}" "${PACKAGES[@]}" | \
     grep -e 'to /build/' | \
     sed -n -E '/^\[ebuild /{s:^[^]]+\] +::;s: .*::;p}' | \
-    grep -E '/(chromeos-config.*|coreboot-private-files.*|tast-build-deps)$' | \
+    grep -E '/(coreboot-private-files.*|tast-build-deps)$' | \
     sort -u ) )
 
   MOD_PKGS=()