[HDRenderPipelineEditor] Removed unused field

ScriptableRenderPipeline/HDRenderPipeline/HDRP/HDRenderPipelineAsset.cs

 
         [SerializeField]
         public SubsurfaceScatteringSettings sssSettings;
-        ISerializationCallbackReceiver m_SerializationCallbackReceiverImplementation;
 
         public override Shader GetDefaultShader()
         {