Revert "MLBEDSW-3645 4D class for op ifm/ofm shapes"

This reverts commit bf31d647dc5df47410ee577b12427ddf076d816b.

Reason for revert: <INSERT REASONING HERE>

Change-Id: I7b6c585b7658f94dbaa916c2b6bfe9fb463b8d37
diff --git a/ethosu/vela/test/test_graph_optimiser.py b/ethosu/vela/test/test_graph_optimiser.py
index 7fdc4bd..4537741 100644
--- a/ethosu/vela/test/test_graph_optimiser.py
+++ b/ethosu/vela/test/test_graph_optimiser.py
@@ -21,7 +21,6 @@
 from ethosu.vela.graph_optimiser import convert_batched_fc_shape
 from ethosu.vela.operation import Op
 from ethosu.vela.tensor import create_const_tensor
-from ethosu.vela.tensor import Shape4D
 from ethosu.vela.tensor import Tensor
 from ethosu.vela.test import testutil
 
@@ -36,8 +35,8 @@
 
     ifm.consumer_list.append(op)
 
-    op.ifm_shapes.append(Shape4D([4, 1, 1, 8]))
-    op.ofm_shapes.append(Shape4D([4, 1, 1, 8]))
+    op.ifm_shapes.append([4, 1, 1, 8])
+    op.ofm_shapes.append([4, 1, 1, 8])
 
     prev_op = op.clone()
     prev_op.ifm_shapes = op.ifm_shapes