Windows: Properly set `mouse_monitor` instead of shadowing it

GCC was raising a warning about unused variable, but it's actually meant
to be used in the destructor for deinit.

platform/windows/display_server_windows.cpp

@@ -3596,12 +3596,11 @@ DisplayServerWindows::DisplayServerWindows(const String &p_rendering_driver, Win
 			return;
 		}
 
-		//gl_manager->set_use_vsync(current_videomode.use_vsync);
 		RasterizerGLES3::make_current();
 	}
 #endif
 
-	HHOOK mouse_monitor = SetWindowsHookEx(WH_MOUSE, ::MouseProc, nullptr, GetCurrentThreadId());
+	mouse_monitor = SetWindowsHookEx(WH_MOUSE, ::MouseProc, nullptr, GetCurrentThreadId());
 
 	Point2i window_position(
 			(screen_get_size(0).width - p_resolution.width) / 2,