Remove NodePreviewView as it is no longer used

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/NodePreviewView.cs.meta

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MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/NodePreviewView.cs

-using UnityEngine;
-using UnityEngine.Experimental.UIElements;
-
-namespace UnityEditor.MaterialGraph.Drawing
-{
-    public class NodePreviewView : Image
-    {
-        public NodePreviewPresenter data;
-
-        public override void DoRepaint()
-        {
-            Debug.Log("DoRepaint");
-            image = data.Render(new Vector2(200, 200));
-            base.DoRepaint();
-        }
-    }
-}