Removes columns in feature matrix where all the values are the same.
feature_matrix (pd.DataFrame) – DataFrame whose columns are feature names and rows are instances.
features (list[featuretools.FeatureBase] or list[str], optional) – List of features to select.
count_nan_as_value – If True, missing values will be counted as their own unique value.
If set to False, a feature that has one unique value and all other
data missing will be removed from the feature matrix. Defaults to False.