test(bigtable): temporarily disable real-service system tests, keep emulated

[mutianf]

Summary

Temporarily disables the system_default (real Cloud Bigtable service) system-test parametrization for google-cloud-bigtable, leaving system_emulated running.

The system nox session previously ran both system_default and system_emulated. This drops system_default from the parametrize list so only the emulator-backed system tests run.

A TODO is left in noxfile.py to re-enable system_default once the real-service system tests are green again. The system_default function itself is left intact (still referenced from test_map), so re-enabling is a one-line revert.

Change

 @nox.parametrize(
     "test_type",
-    ["system_default", "system_emulated"],
+    # TODO: Re-enable "system_default" once the real-service system tests are
+    # green again. Only the emulated system tests run for now.
+    ["system_emulated"],
 )

See follow up issue #18162

[gemini-code-assist]

Code Review

This pull request updates the noxfile.py configuration for google-cloud-bigtable to temporarily disable the 'system_default' test type, running only 'system_emulated' tests until the real-service system tests are green again. I have no feedback to provide as there are no review comments.

[daniel-sanche]

It looks like this PR added some clean-up code to the system tests, that isn't scoped to the emulator. So it is still failing the quota check

I'll have to look into these quota issues. But if you need to disable the system tests today, it looks like the emulator will have to be disabled too