Remove defunct extension_module() meta tests

Author: honno

array_api_tests/meta/test_utils.py

@@ -13,15 +13,6 @@
     oneway_broadcastable_shapes,
     oneway_promotable_dtypes,
 )
-from ..test_signatures import extension_module
-
-
-def test_extension_module_is_extension():
-    assert extension_module("linalg")
-
-
-def test_extension_func_is_not_extension():
-    assert not extension_module("linalg.cross")
 
 
 @pytest.mark.parametrize(