Revert "Improve and fix spline (#610)"

This reverts commit 0844282.

Author: GiovanniCanali

docs/source/_rst/_code.rst

@@ -95,7 +95,6 @@ Models
     MultiFeedForward <model/multi_feed_forward.rst>
     ResidualFeedForward <model/residual_feed_forward.rst>
     Spline <model/spline.rst>
-    SplineSurface <model/spline_surface.rst>
     DeepONet <model/deeponet.rst>
     MIONet <model/mionet.rst>
     KernelNeuralOperator <model/kernel_neural_operator.rst>

docs/source/_rst/model/spline_surface.rst

@@ -26,7 +26,6 @@
 from .average_neural_operator import AveragingNeuralOperator
 from .low_rank_neural_operator import LowRankNeuralOperator
 from .spline import Spline
-from .spline_surface import SplineSurface
 from .graph_neural_operator import GraphNeuralOperator
 from .pirate_network import PirateNet
 from .equivariant_graph_neural_operator import EquivariantGraphNeuralOperator