Remove `my_result_of_t` in favor of `std::invoke_result_t`

[Enmk]

Kludged to support both C++ 17 and C++ 20, but now since we've completely switched to C++20 in 3.0 branch, it is safe to remove it.

clickhouse-cpp/ut/utils_meta.h

Line 37 in ca8a430

using my_result_of_t = std::invoke_result_t<F, ArgTypes...>;