stripping mixed lighting variants

Assets/Data/LightweightAsset.asset

   m_ShadowNormalBias: 1
   m_SoftShadowsSupported: 1
   m_SupportsDynamicBatching: 0
-  m_MixedLightingSupported: 1
+  m_MixedLightingSupported: 0
   m_ShadowType: 1
   m_LocalShadowsSupported: 0
   m_LocalShadowsAtlasResolution: 256