Remove user invitations from LCS docs - 7.0

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 7.0.x
• Component/s: Connected Services (LCS)
• Labels: None
• Git Pull Request: https://github.com/sez11a/liferay-docs/pull/2324

The user invitations feature has been removed from LCS. Remove it from the docs as well.