Disable ExCamConfigInterface Pixel Perfect option

This causes low performance in 2017.2

Author: lawwong

Assets/HTC.UnityPlugin/ViveInputUtility/Resources/VIUExCamConfigInterface.prefab

@@ -9643,7 +9643,7 @@ Canvas:
   m_RenderMode: 1
   m_Camera: {fileID: 2091452}
   m_PlaneDistance: 1
-  m_PixelPerfect: 1
+  m_PixelPerfect: 0
   m_ReceivesEvents: 1
   m_OverrideSorting: 0
   m_OverridePixelPerfect: 0