sparse_set: discard the no longer necessary operator!=

src/entt/entity/sparse_set.hpp

@@ -107,11 +107,6 @@ template<typename Container>
     return lhs.index() == rhs.index();
 }
 
-template<typename Container>
-[[nodiscard]] constexpr bool operator!=(const sparse_set_iterator<Container> &lhs, const sparse_set_iterator<Container> &rhs) noexcept {
-    return !(lhs == rhs);
-}
-
 template<typename Container>
 [[nodiscard]] constexpr bool operator<(const sparse_set_iterator<Container> &lhs, const sparse_set_iterator<Container> &rhs) noexcept {
     return lhs.index() > rhs.index();