Remove normals for ConvexHullNode

They are rendered flat, so no need to store the normals

CURA-7106

cura/Scene/ConvexHullNode.py

@@ -61,6 +61,7 @@ class ConvexHullNode(SceneNode):
                 if hull_mesh_builder.addConvexPolygon(
                     self._hull.getPoints()[::],  # bottom layer is reversed
                     self._mesh_height, color = self._color):
+                    hull_mesh_builder.resetNormals()
 
                     hull_mesh = hull_mesh_builder.build()
                     self.setMeshData(hull_mesh)
@@ -68,7 +69,7 @@ class ConvexHullNode(SceneNode):
                 if hull_mesh_builder.addConvexPolygonExtrusion(
                     self._hull.getPoints()[::-1],  # bottom layer is reversed
                     self._mesh_height - thickness, self._mesh_height, color = self._color):
-
+                    hull_mesh_builder.resetNormals()
                     hull_mesh = hull_mesh_builder.build()
                     self.setMeshData(hull_mesh)