Remove codeowners from expected_doxygen_warnings.txt

[johnnonweiler]

When warnings are removed from expected_doxygen_warnings.txt, it should be adequate for the codeowners of the relevant source files to review the change, and it seems better not to also require the codeowners of the scripts folder.

(Hopefully, we won't generally be adding to the list of expected Doxygen warnings, but we are planning to fix some warnings and remove them from the list.)

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[allredj]

🚫
This PR failed Diffblue compatibility checks (cbmc commit: 91da8ff).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/90707394
Status will be re-evaluated on next push.
Please contact @peterschrammel, @thk123, or @allredj for support.

Common spurious failures:

• the cbmc commit has disappeared in the mean time (e.g. in a force-push)
• the author is not in the list of contributors (e.g. first-time contributors).

The incompatibility may have been introduced by an earlier PR. In that case merging this
PR should be avoided unless it fixes the current incompatibility.

[chrisr-diffblue]

I think that makes reasonable sense.