Remove improper use of `__declspec(allocator)` (#2328)

stl/inc/xmemory

@@ -832,8 +832,7 @@ public:
     }
 
 #if _HAS_CXX23
-    _NODISCARD constexpr __declspec(allocator) allocation_result<_Ty*> allocate_at_least(
-        _CRT_GUARDOVERFLOW const size_t _Count) {
+    _NODISCARD constexpr allocation_result<_Ty*> allocate_at_least(_CRT_GUARDOVERFLOW const size_t _Count) {
         return {allocate(_Count), _Count};
     }
 #endif // _HAS_CXX23