build_plan: Use SlimBuildCfg to determine slim-eligible file patterns.

Replace hard-coded list of slim-eligible file patterns with
SlimBuildConfig.

BUG=chromium:1126323
TEST=./run_tests.sh and local run

Change-Id: I86348bfe7c503adf4514d3f60fe5e9cf3781a3e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/go/+/2401916
Commit-Queue: Navil Perez <navil@google.com>
Tested-by: Navil Perez <navil@google.com>
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
5 files changed