personal: Downgrade from ClusterableModel to Model

We no longer need modelcluster for Groups and Contact, as they are
edited seperately. Downgrade base class from
modelcluster.models.ClusterableModel to django.db.models.Model

mpicms/personal/models.py

@@ -8,7 +8,6 @@
 from wagtail.search import index
 from wagtail.snippets.edit_handlers import SnippetChooserPanel
 
-from modelcluster.models import ClusterableModel
 from modelcluster.fields import ParentalKey
 
 
@@ -75,7 +74,7 @@ class Meta:
 
 
 @register_snippet
-class Group(index.Indexed, ClusterableModel):
+class Group(index.Indexed, models.Model):
     slug = models.CharField(_("slug"), max_length=254)
     name = models.CharField(_("name"), max_length=254, blank=True)
     priority = models.PositiveSmallIntegerField(
@@ -102,18 +101,7 @@ class Meta:  # noqa
 
 
 @register_snippet
-class Contact(index.Indexed, ClusterableModel):
-    """
-    A Django model to store People objects.
-    It uses the `@register_snippet` decorator to allow it to be accessible
-    via the Snippets UI (e.g. /admin/snippets/base/people/)
-    `People` uses the `ClusterableModel`, which allows the relationship with
-    another model to be stored locally to the 'parent' model (e.g. a PageModel)
-    until the parent is explicitly saved. This allows the editor to use the
-    'Preview' button, to preview the content, without saving the relationships
-    to the database.
-    https://github.com/wagtail/django-modelcluster
-    """
+class Contact(index.Indexed, models.Model):
     title = models.CharField(_("title"), max_length=15, blank=True)
     first_name = models.CharField(_("first name"), max_length=50, blank=True)
     last_name = models.CharField(_("last name"), max_length=50, blank=True)