Linearise the detail includes

The current organisation of the headers has been making less and less
sense over the years, so to simplify things, I'm just going to combine
them into a single header. This change will make it easier to do that.

include/boost/unordered/detail/map.hpp

@@ -5,7 +5,6 @@
 
 #include <boost/unordered/unordered_map_fwd.hpp>
 #include <boost/unordered/detail/equivalent.hpp>
-#include <boost/unordered/detail/unique.hpp>
 
 namespace boost { namespace unordered { namespace detail {
     template <typename A, typename K, typename M, typename H, typename P>