Note about "Two merge requests in the same project cannot depend on each other" no longer valid

What product or feature(s) affected?
- Merge Request dependencies
What docs or doc section affected? Include links or paths.
- https://docs.gitlab.com/ee/user/project/merge_requests/merge_request_dependencies.html
Is there a problem with a specific document, or a feature/process that's not addressed sufficiently in docs?
- Yes. The note about "Two merge requests in the same project cannot depend on each other" is no longer valid as of 12.4 release

Any concepts, procedures, reference info we could add to make it easier to successfully use GitLab?
- See https://about.gitlab.com/blog/2019/10/22/gitlab-12-4-released/#merge-request-dependencies (last sentance paragraph 2)
- See #13177 (closed), specifically !16799 (merged)

Remove the note:

Note: A merge request can only depend on merge requests in a different project. Two merge requests in the same project cannot depend on each other.