pandas.Series.nunique.__name__ changes after running dfs

`featuretools.dfs()` changes `pandas.Series.nunique.__name__` when executing an aggregation primitive containing `num_unique`.

Example:
```python
from pandas import DataFrame, Series
import featuretools as ft
from woodwork.logical_types import Categorical

df = DataFrame({"index": [1,2,3,4,5],
"A": ["cat", "dog", "cat", "horse", "monkey"],
"Group": ["X", "X", "Y", "Y", "Y"]})

es = ft.EntitySet(id="test")
es = es.add_dataframe(dataframe_name="df", index="index", dataframe=df, logical_types={"A": Categorical})
es = es.normalize_dataframe(base_dataframe_name="df", new_dataframe_name="group", index="Group")

assert Series.nunique.__name__ == "nunique"

feature_matrix, feature_defs = ft.dfs(
entityset=es,
target_dataframe_name="group",
agg_primitives=['num_unique'],
trans_primitives=[]
)

assert Series.nunique.__name__ != "nunique"
```