Fixed missing or unused imports

src/pretix/presale/urls.py

@@ -1,4 +1,4 @@
-from django.conf.urls import include, url
+from django.conf.urls import url
 
 import pretix.presale.views.cart
 import pretix.presale.views.checkout

src/pretix/presale/views/order.py

@@ -1,7 +1,6 @@
 from datetime import timedelta
 
 from django.contrib import messages
-from django.core.exceptions import PermissionDenied
 from django.core.urlresolvers import reverse
 from django.http import Http404
 from django.shortcuts import redirect