chore(ci): remove unused reset-test-account workflow

[noel]

What

Removes .github/workflows/reset-test-account.yml.

Why

Zero runs in this repo's history across all 5 configured environments (snowflake-azure-standard, snowflake-gcp-standard, snowflake-aws-standard, snowflake-aws-enterprise, snowflake-aws-business-critical). It's not called by any other workflow (workflow_call trigger was declared but nothing in-repo invokes it).

The underlying tooling it wrapped (tools/manage_test_account.py, make reset-test-account) is unaffected and stays documented in TESTING.md for local/manual use.

[github-actions]

Review of PR #81

No issues found.

This PR only deletes .github/workflows/reset-test-account.yml. I checked for anything that depended on it:

• No other workflow under .github/ calls it with workflow_call or refers to it by name.
• The reset-test-account hits in Makefile, TESTING.md and tools/ are the local make reset-test-account target and the Blueprint name. They don't use the workflow.
• The Python entry points (tools/manage_test_account.py, including teardown-and-reset) are unchanged, so the reset can still be run manually.

Deleting the workflow also stops it from exposing the TEST_SNOWFLAKE_* secrets to a CI job, which is a small security gain.