Revert "Implement LWG 2221 - No formatted output operator for nullptr."

This reverts r342566 as it causes on bots linker errors like

> Undefined symbols for architecture i386:
>   "std::__1::basic_ostream<char, std::__1::char_traits<char> >::operator<<(std::nullptr_t)", referenced from:

llvm-svn: 342599