Removed an unnecessary models file in the admin_scripts tests.

tests/admin_scripts/models.py

-from django.db import models
-from django.utils.encoding import python_2_unicode_compatible
-
-
-@python_2_unicode_compatible
-class Article(models.Model):
-    headline = models.CharField(max_length=100, default='Default headline')
-    pub_date = models.DateTimeField()
-
-    def __str__(self):
-        return self.headline
-
-    class Meta:
-        ordering = ('-pub_date', 'headline')