Removed unneeded import

wagtail/tests/utils.py

@@ -1,4 +1,4 @@
-from django.contrib.auth.models import User, Permission
+from django.contrib.auth.models import User
 
 # We need to make sure that we're using the same unittest library that Django uses internally
 # Otherwise, we get issues with the "SkipTest" and "ExpectedFailure" exceptions being recognised as errors