removed some unused using statements

Author: StephenHodgson

Assets/MixedRealityToolkit/_Core/Devices/OpenVR/OpenVRDeviceManager.cs

@@ -4,8 +4,6 @@
 using Microsoft.MixedReality.Toolkit.Internal.Definitions.Devices;
 using Microsoft.MixedReality.Toolkit.Internal.Definitions.Utilities;
 using Microsoft.MixedReality.Toolkit.Internal.Interfaces;
-using Microsoft.MixedReality.Toolkit.Internal.Interfaces.InputSystem;
-using Microsoft.MixedReality.Toolkit.Internal.Managers;
 using System;
 using System.Collections.Generic;
 using System.Linq;