[sf.cmath] contains superfluous "Effects:"-clauses

[Eelis]

For example: https://eel.is/c++draft/sf.cmath.riemann.zeta#1

This "Effects:"-clause doesn't specify anything that isn't already specified by the "Returns:"-clause that immediately follows it. If anything, this "Effects:"-clause sounds like an informal commentary on the intentions of the "Returns:"-clause.

[jensmaurer]

Well, having a bit of prose explanation of the gigantic math formula that follows feels helpful to me.