Remove misleading self-issued language that seems to imply that nonce is optional

[Michael Jones]

In bullet 8 of https://openid.net/specs/openid-connect-core-1_0.html#SelfIssuedValidation, the language “If a nonce value was sent in the Authentication Request“ is misleading, and should be removed. Nonce is already required for the Implicit flow at https://openid.net/specs/openid-connect-core-1_0.html#ImplicitAuthRequest - including for response_type=id_token.

This problem was first identified in issue #1265.

[Nat Sakimura]

To be applied in the next errata.

[Michael Jones]

Will be fixed by https://bitbucket.org/openid/connect/pull-requests/336/errata-removed-misleading-self-issued

[Michael Jones]

Addressed by the now-merged PR