MAINT: remove `NUMPY_EXPERIMENTAL_ARRAY_FUNCTION` env var

As discussed in
https://mail.python.org/archives/list/numpy-discussion@python.org/thread/UKZJACAP5FUG7KP2AQDPE4P5ADNWLOHZ/

This flag was always meant to be temporary, and cleaning it up is
long overdue.

3 files changed, 18 insertions, 34 deletions

diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index 405790025..f0f374f97 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -4910,23 +4910,22 @@ def trapz(y, x=None, dx=1.0, axis=-1):
     return ret
 
 
-if overrides.ARRAY_FUNCTION_ENABLED:
-    # If array-function is enabled (normal), we wrap everything into a C
-    # callable, which has no __code__ or other attributes normal Python funcs
-    # have.  SciPy however, tries to "clone" `trapz` into a new Python function
-    # which requires `__code__` and a few other attributes.
-    # So we create a dummy clone and copy over its attributes allowing
-    # SciPy <= 1.10 to work: https://github.com/scipy/scipy/issues/17811
-    assert not hasattr(trapz, "__code__")
-
-    def _fake_trapz(y, x=None, dx=1.0, axis=-1):
-        return trapz(y, x=x, dx=dx, axis=axis)
-
-    trapz.__code__ = _fake_trapz.__code__
-    trapz.__globals__ = _fake_trapz.__globals__
-    trapz.__defaults__ = _fake_trapz.__defaults__
-    trapz.__closure__ = _fake_trapz.__closure__
-    trapz.__kwdefaults__ = _fake_trapz.__kwdefaults__
+# __array_function__ has no __code__ or other attributes normal Python funcs we
+# wrap everything into a C callable. SciPy however, tries to "clone" `trapz`
+# into a new Python function which requires `__code__` and a few other
+# attributes. So we create a dummy clone and copy over its attributes allowing
+# SciPy <= 1.10 to work: https://github.com/scipy/scipy/issues/17811
+assert not hasattr(trapz, "__code__")
+
+def _fake_trapz(y, x=None, dx=1.0, axis=-1):
+    return trapz(y, x=x, dx=dx, axis=axis)
+
+
+trapz.__code__ = _fake_trapz.__code__
+trapz.__globals__ = _fake_trapz.__globals__
+trapz.__defaults__ = _fake_trapz.__defaults__
+trapz.__closure__ = _fake_trapz.__closure__
+trapz.__kwdefaults__ = _fake_trapz.__kwdefaults__
 
 
 def _meshgrid_dispatcher(*xi, copy=None, sparse=None, indexing=None):
diff --git a/numpy/lib/shape_base.py b/numpy/lib/shape_base.py
index 154faa1dd..5d8a41bfe 100644
--- a/numpy/lib/shape_base.py
+++ b/numpy/lib/shape_base.py
@@ -643,10 +643,6 @@ def column_stack(tup):
            [3, 4]])
 
     """
-    if not overrides.ARRAY_FUNCTION_ENABLED:
-        # reject non-sequences (and make tuple)
-        tup = _arrays_for_stack_dispatcher(tup)
-
     arrays = []
     for v in tup:
         arr = asanyarray(v)
@@ -713,10 +709,6 @@ def dstack(tup):
            [[3, 4]]])
 
     """
-    if not overrides.ARRAY_FUNCTION_ENABLED:
-        # reject non-sequences (and make tuple)
-        tup = _arrays_for_stack_dispatcher(tup)
-
     arrs = atleast_3d(*tup)
     if not isinstance(arrs, list):
         arrs = [arrs]
diff --git a/numpy/lib/tests/test_twodim_base.py b/numpy/lib/tests/test_twodim_base.py
index 141f508fd..eb008c600 100644
--- a/numpy/lib/tests/test_twodim_base.py
+++ b/numpy/lib/tests/test_twodim_base.py
@@ -4,20 +4,14 @@
 from numpy.testing import (
     assert_equal, assert_array_equal, assert_array_max_ulp,
     assert_array_almost_equal, assert_raises, assert_
-    )
-
+)
 from numpy import (
     arange, add, fliplr, flipud, zeros, ones, eye, array, diag, histogram2d,
     tri, mask_indices, triu_indices, triu_indices_from, tril_indices,
     tril_indices_from, vander,
-    )
-
+)
 import numpy as np
 
-
-from numpy.core.tests.test_overrides import requires_array_function
-
-
 import pytest
 
 
@@ -283,7 +277,6 @@ class TestHistogram2d:
         assert_array_equal(H, answer)
         assert_array_equal(xe, array([0., 0.25, 0.5, 0.75, 1]))
 
-    @requires_array_function
     def test_dispatch(self):
         class ShouldDispatch:
             def __array_function__(self, function, types, args, kwargs):