boards: m5stack_core2: do not use as default test platform

Only quemu boards are used as default in CI, drop the default property
from this one.

(cherry picked from commit 2fbcb46)

Original-Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
GitOrigin-RevId: 2fbcb46
Change-Id: I3c76a4afc0625373fd5cd821cd31b231da37f7ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5003996
Reviewed-by: Fabio Baltieri <fabiobaltieri@google.com>
Tested-by: Fabio Baltieri <fabiobaltieri@google.com>
Commit-Queue: Fabio Baltieri <fabiobaltieri@google.com>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>

boards/xtensa/m5stack_core2/m5stack_core2.yaml

@@ -14,7 +14,6 @@ supported:
   - pinmux
   - nvs
 testing:
-  default: true
   ignore_tags:
     - net
     - bluetooth