DOC: Series.count remove mention of "level"

[lukemanley]

similar to #54395 (I should have checked Series.count in that PR)

[lukemanley]

Looks like this is failing due to the following inconsistency in return types for boolean arrays vs other arrays:

In [1]: import pandas as pd

In [2]: type(pd.Series([1, 0 , 1]).std())
Out[2]: float

In [3]: type(pd.Series([True, False, True]).std())
Out[3]: numpy.float64

This is tested behavior in test_reductions_return_types.

[mroeschke]

Thanks @lukemanley