remove refresh token requirement on RPs

[aaronpk]

The OIDC SL1 profile currently says that RPs "MUST support refresh tokens and their rotation". I don't think this makes much sense now that access tokens are only for OP resources. I think we should just remove this requirement.

[deansaxe]

Agreed. I think this line can be removed.

[aaronpk]

Discussed and merged on the Aug 26 call.