test_platform: Delete deprecated field

BUG=chromium:1161539
TEST=./generate.sh

Cq-Depend: chromium:2601299
Change-Id: I1cb3f9f4b3f92fb112c899abc41ab52b934d1f57
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2601243
Reviewed-by: Brigit Rossbach <brigitr@google.com>
Commit-Queue: Prathmesh Prabhu <pprabhu@google.com>
2 files changed