Basic - 4 misplaced normative text for check session endpoint

[Former user]

Section 4 says:

"The id_token and Check Session Endpoint MUST be used to validate the identity of a session."

Not clear why a normative MUST that concerns the check session endpoint is placed under the Userinfo endpoint section.

[Nat Sakimura]

Delete the paragraph as it was dealt with #83.

[Edmund Jay]

fixes #84

→ 05d2338fac1b