util: remove memory debug
Here's another approach to solving the problem in !3844 (merged), where the entire mechanism is removed instead.
I think this approach makes a bit more sense, there's no need to treat Windows differently, I think; the MSVC run-time has great memory-debugging tools (much better than these ones IMO), and as MinGW also uses MSVCRT, this probably applies to all Windows builds AFAICT. I haven't checked what Clang does, but I would assume it does the same thing.
This also fixes the problem that !3845 (closed) solves as well, but takes it all away in one go.