Remove TLD validation from cluster domain

What does this MR do?

This validation was introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24368 but it is undesirable for a couple of reasons:

1. It may make sense for use cases in internal applications that this domain is not actually a valid TLD
2. It also led to a regression because perfectly valid TLDs are not known by the validator we are using (eg. .live #57650 (closed)) . We could have updated the gem to fix that but I don't believe we actually want this validation anyway.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• [-] Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #57650 (closed)