Don't import stuff we don't need

pretix_public_registrations/signals.py

 from django import forms
 from django.dispatch import receiver
 from django.template.loader import get_template
-from django.utils.translation import ugettext_lazy as _, get_language
+from django.utils.translation import ugettext_lazy as _
 from django.urls import resolve, reverse
 from django_gravatar.helpers import get_gravatar_url
 from i18nfield.strings import LazyI18nString