Remove/update util/concepts.h macros after C++20

The macros in util/concepts.h were meant as transitional tools smooth over template restrictions until c++20 support was made available.

Once we're onto C++20, we should replace the template/requires macros and re-evaluate the necessity of the REQUIRES_OUT_OF_LINE_DEF and REQURES_FOR_NON_TEMPLATE.

We should also think about prefixing any macros we retain, as mentioned in SERVER-47912