Remove outdated shibboleth integration

Purpose

The shibboleth documentation is old and doesn’t reflect current state.

I, personally, don’t know what it should say, however several clients of mine, after wasting time on this approach, switch to a SAML approach, and all is well.

I think they would have saved time if this page did not exist.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers