[func.wrap.ref.class] Rename the parameter `c` in `constant_wrapper<c, F>`?

[hewillk]

https://eel.is/c++draft/func.wrap.ref#class:

template<auto c, class F> constexpr function_ref(constant_wrapper<c, F>) noexcept;

The use of a lowercase c as the template parameter name here seems a bit odd to me; in libraries, we rarely seem to use a single lowercase letter as a template parameter. The c here also overlaps with the c in cv.

Would it be better to use X, or even _ (because we didn't use it at all)?