Don’t create new organisations with no crown status

We need the crown status set so that we can let them accept the
agreement online.

app/main/forms.py

@@ -596,10 +596,13 @@ class OrganisationTypeForm(StripWhitespaceForm):
 
 class NewOrganisationForm(
     RenameOrganisationForm,
-    OrganisationTypeForm,
+    OrganisationOrganisationTypeForm,
     OrganisationCrownStatusForm,
 ):
-    pass
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        # Don’t offer the ‘not sure’ choice
+        self.crown_status.choices = self.crown_status.choices[:-1]
 
 
 class FreeSMSAllowance(StripWhitespaceForm):