Remove an erroneous import in the unit tests and add extra test dependencies.

quapy/tests/test_modsel.py

@@ -4,7 +4,6 @@ import numpy as np
 from sklearn.linear_model import LogisticRegression
 
 import quapy as qp
-import util
 from quapy.method.aggregative import PACC
 from quapy.model_selection import GridSearchQ
 from quapy.protocol import APP

setup.py

@@ -125,6 +125,7 @@ setup(
     # projects.
     extras_require={  # Optional
        'bayes': ['jax', 'jaxlib', 'numpyro'],
+       'tests': ['certifi'],
     },
 
     # If there are data files included in your packages that need to be