purge _get_args helper func

[drammock]

closes #11089

@larsoner in all but one case, a simple signature(f).parameters (or list(signature(f).parameters) was sufficient. IMO the helper function is not really needed, but if you disagree feel free to close this without merging.

[drammock]

These failures passed for me locally... turns out I had scipy 1.8.x and they fail with 1.9.x. Will fix:

_________________________ test_ica_additional[picard] __________________________
mne/preprocessing/tests/test_ica.py:789: in test_ica_additional
    for name, func in get_score_funcs().items():
mne/preprocessing/ica.py:121: in get_score_funcs
    assert 'pearsonr' in score_funcs
E   AssertionError
_________________________ test_ica_additional[fastica] _________________________
mne/preprocessing/tests/test_ica.py:789: in test_ica_additional
    for name, func in get_score_funcs().items():
mne/preprocessing/ica.py:121: in get_score_funcs
    assert 'pearsonr' in score_funcs
E   AssertionError
_______________________________ test_ica_labels ________________________________
mne/preprocessing/tests/test_ica.py:1374: in test_ica_labels
    ica.find_bads_eog(raw, l_freq=None, h_freq=None)
<decorator-gen-447>:12: in find_bads_eog
    ???
mne/preprocessing/ica.py:1889: in find_bads_eog
    self.labels_['eog'], scores = self._find_bads_ch(
mne/preprocessing/ica.py:1376: in _find_bads_ch
    scores += [self.score_sources(
<decorator-gen-443>:12: in score_sources
    ???
mne/preprocessing/ica.py:1318: in score_sources
    scores = _find_sources(sources, target, score_func)
mne/preprocessing/ica.py:2367: in _find_sources
    score_func = get_score_funcs().get(score_func, score_func)
mne/preprocessing/ica.py:121: in get_score_funcs
    assert 'pearsonr' in score_funcs
E   AssertionError

[drammock]

OK those tests pass locally now for me with scipy 1.8.0 and 1.9.1 so hopefully CIs are happy now

[agramfort]

@britta-wstnr I let you click the auto-merge button if it's ok for you.

[agramfort]

thx @drammock