Revert "Merge branch '273765-disallow-editing-project-level-mr-settings' into 'master'"

What does this MR do?

As part of investigating the staging incident gitlab-com/gl-infra/production#3010 (closed) we have a strong suspicion that !46637 (merged) might be the culprit.

We see increased traffic to Gitaly resulting from evaluating merge request approval rules, and that's the only merge request related to this part of the code that went in as part of the deploy, so even though we can't pinpoint the problematic code at this point, we will try reverting it, deploy the revert to staging and see if things get better.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team