Remove staging env stub to avoid side effects

What does this MR do and why?

We have tests that clear the Redis connection pools and stubbing the environment to be staging reinitializes them with incorrect arguments. See gitlab-org/quality/engineering-productivity/master-broken-incidents#4077 (closed)

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.