Remove unused imports

aleksis/apps/csv_import/preferences.py

 from django.utils.translation import gettext_lazy as _
 
-import pycountry
 from dynamic_preferences.preferences import Section
-from dynamic_preferences.types import ChoicePreference, ModelChoicePreference, StringPreference
+from dynamic_preferences.types import ModelChoicePreference, StringPreference
 
 from aleksis.core.models import Group, GroupType
 from aleksis.core.registries import site_preferences_registry