chore: reduce diffs to GasFeeController.test.ts introduced by 2b1841c (#4463)

## Explanation
Commit 2b1841c introduced [unnecessary changes to
`GasFeeController.test.ts`](2b1841c#diff-46b4165a6fef6c662829473a7ae3dd5c12454ca7ea811b539c0e88dc464f7e3b),
complicating the process of rebasing and merging subsequent changes to
this file.

To see the net diffs to `GasFeeController.test.ts` in this branch, you
can compare that file to 2b1841c's parent commit, ca683e8:
  ```bash
git diff ca683e8...djb/gas-fee-tests
packages/gas-fee-controller/src/GasFeeController.test.ts
  ```
## References

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## Changelog

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## Checklist

- [ ] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've highlighted breaking changes using the "BREAKING" category
above as appropriate

Author: dbrans