Resolve "Remove Gitlab::GitAccess#authed_via_jwt?"

What does this MR do?

Removes the following code from lib/gitlab/git_access.rb as it's no longer needed:

def authed_via_jwt?
  false
end

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/51267 https://gitlab.com/gitlab-org/gitlab-ee/issues/6533

Does this MR meet the acceptance criteria?

• [ ] Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines~~
• Conforms to the style guides~~
• [ ] Conforms to the database guides

Closes #51267 (closed)