Remove custom wagtail page form

THe older page form allowed to change segment settings inline but since
support for this was temporarily removed in an earlier commit we can
clean this up too

src/wagtail_personalisation/models.py

@@ -7,13 +7,12 @@ from django.utils.functional import cached_property
 from django.utils.translation import ugettext_lazy as _
 from modelcluster.fields import ParentalKey
 from modelcluster.models import ClusterableModel
-from wagtail.wagtailcore.models import Page
 from wagtail.utils.decorators import cached_classmethod
 from wagtail.wagtailadmin.edit_handlers import (
     FieldPanel, FieldRowPanel, InlinePanel, MultiFieldPanel, ObjectList,
     PageChooserPanel, TabbedInterface)
+from wagtail.wagtailcore.models import Page
 
-from wagtail_personalisation.forms import AdminPersonalisablePageForm
 from wagtail_personalisation.rules import AbstractBaseRule
 from wagtail_personalisation.utils import count_active_days
 
@@ -115,10 +114,6 @@ class PersonalisablePageMetadata(ClusterableModel):
     segment = models.ForeignKey(
         Segment, related_name='page_metadata', null=True, blank=True)
 
-    is_segmented = models.BooleanField(default=False)
-
-    base_form_class = AdminPersonalisablePageForm
-
     @cached_property
     def has_variations(self):
         """Return a boolean indicating whether or not the personalisable page
@@ -170,8 +165,7 @@ class PersonalisablePageMetadata(ClusterableModel):
             PersonalisablePageMetadata.objects.create(
                 canonical_page=page,
                 variant=new_page,
-                segment=segment,
-                is_segmented=True)
+                segment=segment)
         return new_page
 
     def variants_for_segments(self, segments):