CI: api.test_api.TestPDApi.test_api fails irrelevantly
#### Problem description

In the pull request #26940, I have changed a piece of code in `pandas/_libs/window.pyx`. Tests pass successfully (including those in tests/api) on my local but not on CI. It seems that `hard_dependencies, dependency, missing_dependencies` are on the pd namespace and not deleted as supposed (see [here](https://github.com/pandas-dev/pandas/blob/master/pandas/__init__.py#L17)). But I don't think changes in #26940 cause this assertion error.

#### Error ([Here](https://travis-ci.org/pandas-dev/pandas/jobs/547916861#L2443))
```python
=================================== FAILURES ===================================
______________________________ TestPDApi.test_api ______________________________
[gw1] linux -- Python 3.7.3 /home/travis/miniconda3/envs/pandas-dev/bin/python
self = <pandas.tests.api.test_api.TestPDApi object at 0x7f2145f522e8>
    def test_api(self):
    
        self.check(pd,
                   self.lib + self.misc +
                   self.modules + self.deprecated_modules +
                   self.classes + self.deprecated_classes +
                   self.deprecated_classes_in_future +
                   self.funcs + self.funcs_option +
                   self.funcs_read + self.funcs_to +
                   self.deprecated_funcs_in_future +
                   self.deprecated_funcs + self.private_modules,
>                  self.ignored)
pandas/tests/api/test_api.py:113: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
pandas/tests/api/test_api.py:18: in check
    tm.assert_almost_equal(result, expected)
pandas/util/testing.py:325: in assert_almost_equal
    **kwargs)
pandas/_libs/testing.pyx:65: in pandas._libs.testing.assert_almost_equal
    cpdef assert_almost_equal(a, b,
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
>   raise_assert_detail(obj, '{0} length are different'.format(obj),
E   AssertionError: Iterable are different
E   
E   Iterable length are different
E   [left]:  132
E   [right]: 129
E   [diff]: ['dependency', 'missing_dependencies', 'hard_dependencies']
pandas/_libs/testing.pyx:163: AssertionError
```