Remove legacy role fields.

biscuit/core/models.py

@@ -3,8 +3,5 @@ from django.db import models
 
 
 class Person(AbstractUser):
-    is_student = models.BooleanField(default=False)
-    is_teacher = models.BooleanField(default=False)
-
     def __str__(self):
         return '%s, %s' % (self.last_name, self.first_name)