Fix compile error

Author: lawwong

Assets/HTC.UnityPlugin/ViveInputUtility/Scripts/Misc/OculusVRExtension/VIUOvrAvatar.cs

@@ -1,4 +1,6 @@
-using Oculus.Avatar;
+#if VIU_OCULUSVR_AVATAR
+using Oculus.Avatar;
+#endif
 using System;
 using System.Collections;
 using System.Collections.Generic;