Remove local hash_value overload; boost::hash supports array-like types natively.

doc/array/changes.adoc

@@ -16,3 +16,5 @@ http://www.boost.org/LICENSE_1_0.txt
 * Added `noexcept` and `constexpr` as appropriate.
 * Marked obsolete functions as deprecated.
 * Removed obsolete compiler workarounds.
+* Changed `array<T, 0>::begin()`, `cbegin()`, `end()`, `cend()` to return `nullptr`, enabling `constexpr`.
+  This matches the behavior of `std::array`.

include/boost/array.hpp

@@ -395,14 +395,6 @@ namespace boost {
         return arg.elems;
     }
 
-    template <class It> std::size_t hash_range(It, It);
-
-    template<class T, std::size_t N>
-    std::size_t hash_value(const array<T,N>& arr)
-    {
-        return boost::hash_range(arr.begin(), arr.end());
-    }
-
    template <size_t Idx, typename T, size_t N>
    BOOST_CXX14_CONSTEXPR T &get(boost::array<T,N> &arr) BOOST_NOEXCEPT {
        BOOST_STATIC_ASSERT_MSG ( Idx < N, "boost::get<>(boost::array &) index out of range" );