Finish move to platform config repo

dut was already moved to src/config and plan needs to be a platform
versioned construct, which infra depends on, but is not defined or
managed by infra.

This is a step in moving to test planning management that is milestone
versioned under src/config-internal.

Change-Id: I763e409ed93efedccce8f464fc54bc73821436c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2359013
Tested-by: C Shapiro <shapiroc@chromium.org>
Auto-Submit: C Shapiro <shapiroc@chromium.org>
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
Commit-Queue: Sean Abraham <seanabraham@chromium.org>
6 files changed