[SYCL] [Graph] Remove unnecesary SYCL_EXPORT (#19149)

Fixes post-commit windows CI failure introduced by #19045

Author: konradkusiak97

sycl/source/detail/graph/graph_impl.hpp

@@ -953,8 +953,7 @@ class exec_graph_impl {
 
 namespace std {
 template <sycl::ext::oneapi::experimental::graph_state State>
-struct __SYCL_EXPORT
-    hash<sycl::ext::oneapi::experimental::command_graph<State>> {
+struct hash<sycl::ext::oneapi::experimental::command_graph<State>> {
   size_t operator()(const sycl::ext::oneapi::experimental::command_graph<State>
                         &Graph) const {
     auto ID = sycl::detail::getSyclObjImpl(Graph)->getID();