[func.bind] needs de-shalling

[jwakely]

[func.bind.isbind]:

Instantiations Specializations of the is_bind_expression template shall satisfy the Cpp17UnaryTypeTrait requirements (20.15.1). The implementation shall provide provides a definition that has a base characteristic of true_type if T is a type returned from bind, otherwise it shall have has a base characteristic of false_type.

Similarly in [func.bind.isplace].

The Returns: and Remarks: in [func.bind.bind] shouldn't be using "shall", and neither should [func.bind.place] p1 and p2.

[jensmaurer]

I'm not convinced that [func.bind.place] should be de-shalled. After all, users can define their own placeholders (using std::is_placeholder), and presumably those restrictions also apply for user-defined placeholders.