Resolve "Unicorn development settings should match production as much as possible"

What does this MR do?

Copy important changes from unicorn.rb.example to unicorn.rb.example.development. Also remove unneeded configurations and update the comment accordingly. I think REE was long dead.

Are there points in the code the reviewer needs to double check?

Would we break any existing setup? Even so, it would only hit newly installed GDK though. I manually copied the contents to my unicorn.rb and it works fine for me.

Why was this MR needed?

We should use a similar setup with production.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a Backend maintainer

What are the relevant issue numbers?

Closes #49756 (closed)