Use consistent flake8 settings everywhere and fix flake8 issues

src/pretix/control/views/event.py

@@ -336,7 +336,7 @@ class MailSettings(EventSettingsFormView):
                 self.request.event.log_action(
                     'pretix.event.settings', user=self.request.user, data={
                         k: form.cleaned_data.get(k) for k in form.changed_data
-                        }
+                    }
                 )
 
             if request.POST.get('test', '0').strip() == '1':

src/pretix/control/views/orders.py

@@ -13,7 +13,7 @@ from django.views.generic import DetailView, ListView, TemplateView, View
 
 from pretix.base.i18n import language
 from pretix.base.models import (
-    CachedFile, CachedTicket, EventLock, Invoice, Item, ItemVariation, Order,
+    CachedFile, CachedTicket, Invoice, Item, ItemVariation, Order,
     Quota,
 )
 from pretix.base.services import tickets