Remove unused typedef. Refs #8874.

[SVN r85245]

include/boost/unordered/detail/unique.hpp

@@ -334,8 +334,6 @@ namespace boost { namespace unordered { namespace detail {
 
         value_type& operator[](key_type const& k)
         {
-            typedef typename value_type::second_type mapped_type;
-    
             std::size_t key_hash = this->hash(k);
             iterator pos = this->find_node(key_hash, k);