core/command/platform: Remove "mosys platform model" for unibuild

The only remaining usage of this command is in cros_config_setup for
pre-unibuild devices, so we can disable it for unibuild.

BUG=b:187790074
TEST=CQ

Change-Id: Ib56bebee703a43d5eb0fbd44d217123333ac0460
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/mosys/+/4006394
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>
2 files changed