Remove number of arguments from defining Dart FFI

[dkwingsmt]

The number of arguments are not used.

And also, even if we need it in the future, they can be derived at compile time:

template <typename T>
struct function_traits;

template <typename Ret, typename... Args>
struct function_traits<Ret(Args...)>
{
    using params = std::tuple<Args...>;
};

template <typename T>
constexpr std::size_t get_parameter_count() {
    return std::tuple_size<typename function_traits<T>::params>::value;
}

template <typename T>
struct member_function_traits;

template <typename C, typename Ret, typename... Args>
struct member_function_traits<Ret(C::*)(Args...)>
{
    using params = std::tuple<Args...>;
};

template <typename T>
constexpr std::size_t get_member_function_parameter_count() {
    return std::tuple_size<typename member_function_traits<T>::params>::value;
}

(I got the code above with ChatGPT but I verified that they work)

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auto label is removed for flutter/engine/50153, due to - The status or check suite Linux Framework Smoke Tests has failed. Please fix the issues identified (or deflake) before re-applying this label.