Draft: Drop the "ee" URL prefix and landing page

What does this MR do and why?

• Removes the /help landing page () from the Docs website build. It's redundant with the homepage.
• Drops the /ee/ prefix from URLs in that section.

Just a draft! This works locally but won't build on CI until we refactor build_site.rake to use product names/keys rather than the slug property.

• Closes #1712 (closed)
• Closes #1081 (closed)

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Closes #1712 (closed)