Now that Unified Builds are a thing and these boards all use the same EC build, we can eliminate some board configuration duplication. This was made possible by a change allowing a Unified Builds build to specify a shared build target across many models in the same board family discussed on https://b.corp.google.com/issues/64117873 . This configuration is stored in the family's model.dtsi file as explained at: https://chromium.googlesource.com/chromiumos/platform2/+/master/chromeos-config/README.md

This change can be done after we turn down the legacy reef-family builders (such that these config files are no longer used in the legacy builds).