REF: Remove image change percentage function

Remove image change percentage function from the `analysis.utils` module as it is a metric of image similarity rather than a metric of motion.

Co-authored-by: Oscar Esteban <code@oscaresteban.es>

Author: jhlegarreta

nitransforms/tests/test_analysis.py

@@ -10,7 +10,6 @@
 from nitransforms.analysis.utils import (
     compute_fd_from_motion,
     compute_fd_from_transform,
-    compute_percentage_change,
     displacements_within_mask,
     extract_motion_parameters,
     identify_spikes,
@@ -137,34 +136,6 @@ def test_extract_motion_parameters(affine, expected_trans, expected_rot):
         assert np.allclose(params[3:], expected_rot)
 
 
-@pytest.mark.parametrize(
-    "reference, test, mask, expected",
-    [
-        (
-            np.array([[1.0, 2.0], [0.0, 4.0]]),
-            np.array([[2.0, 1.0], [3.0, 8.0]]),
-            np.array([[True, True], [True, True]]),
-            np.array([[(2.0 - 1.0) / 1.0, (1.0 - 2.0) / 2.0], [0, (8.0 - 4.0) / 4.0]]) * 100,
-        ),
-        (
-            np.zeros((2,2)),
-            np.ones((2,2)),
-            np.ones((2,2), dtype=bool),
-            np.zeros((2,2)),
-        ),
-        (
-            np.array([[5, 10], [15, 20]]),
-            np.array([[10, 5], [30, 10]]),
-            np.array([[False, True], [True, False]]),
-            np.array([[0, (5 - 10) / 10], [(30 - 15) / 15, 0]]) * 100,
-        ),
-    ],
-)
-def test_compute_percentage_change_param(reference, test, mask, expected):
-    result = compute_percentage_change(reference, test, mask)
-    np.testing.assert_array_almost_equal(result, expected)
-
-
 def test_identify_spikes(request):
     rng = request.node.rng