[Sycl][Graph] Remove SYCL_EXPORT from template to fix build error (#17005)

PR #16788 broke the windows
post-commit CI when building with `icx`/`icpx`
https://github.com/intel/llvm/actions/runs/13310637099/job/37172065867

```
D:\github\_work\llvm\llvm\build\include\sycl\ext\oneapi\experimental\graph.hpp(577,8): error: 'dllexport' attribute ignored [-Werror,-Wignored-attributes]
  577 | struct __SYCL_EXPORT
      |        ^
D:\github\_work\llvm\llvm\build\include\sycl\detail\export.hpp(23,34): note: expanded from macro '__SYCL_EXPORT'
   23 | #define __SYCL_EXPORT __declspec(dllexport)
      |                                  ^
In file included from D:\github\_work\llvm\llvm\src\sycl\unittests\Extensions\EventMode.cpp:9:
In file included from D:\github\_work\llvm\llvm\build\include\sycl\sycl.hpp:11:
In file included from D:\github\_work\llvm\llvm\build\include\sycl\detail\core.hpp:23:
In file included from D:\github\_work\llvm\llvm\build\include\sycl\queue.hpp:34:
D:\github\_work\llvm\llvm\build\include\sycl\ext\oneapi\experimental\graph.hpp(587,8): error: 'dllexport' attribute ignored [-Werror,-Wignored-attributes]
  587 | struct __SYCL_EXPORT
      |        ^
D:\github\_work\llvm\llvm\build\include\sycl\detail\export.hpp(23,34): note: expanded from macro '__SYCL_EXPORT'
   23 | #define __SYCL_EXPORT __declspec(dllexport)
      |                                  ^
2 errors generated.
```

Fix by not exporting these symbols

Author: fabiomestre

sycl/include/sycl/ext/oneapi/experimental/graph.hpp

@@ -574,8 +574,7 @@ struct __SYCL_EXPORT
 };
 
 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();
@@ -584,8 +583,7 @@ struct __SYCL_EXPORT
 };
 
 template <typename ValueT>
-struct __SYCL_EXPORT
-    hash<sycl::ext::oneapi::experimental::dynamic_parameter<ValueT>> {
+struct hash<sycl::ext::oneapi::experimental::dynamic_parameter<ValueT>> {
   size_t
   operator()(const sycl::ext::oneapi::experimental::dynamic_parameter<ValueT>
                  &DynamicParam) const {