Remove redirects feature toggle docs

What does this MR do?

Remove redirects feature toggle docs

• The toggle itself was removed in gitlab-pages!357 (closed)
• Original docs added in !42011 (merged)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
  • "Any docs-only changes should not have a changelog entry."
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content