[libc++] Merge _LIBCPP_HAS_NO_RANGES into _LIBCPP_HAS_NO_CONCEPTS. NFC.

The macro that opts out of `std::ranges::` functionality is called
`_LIBCPP_HAS_NO_INCOMPLETE_RANGES`, and is unrelated to this macro
which is specifically about _compiler_ support for the _syntax_.

The only non-mechanical diff here is in `<__config>`.

Differential Revision: https://reviews.llvm.org/D118507