changes to reflect PR comments (not finished)

data/model/legacy.py

@@ -2550,17 +2550,12 @@ def unstar_repository(user, repository):
   """ Unstars a repository. """
   try:
     star = (Star
-            .select()
-            .join(Repository)
-            .switch(Star)
-            .join(User)
-            .where(Repository.id == repository.id, User.id == user.id)
-            .get())
+            .delete()
+            .where(Star.repository == repository.id, Star.user == user.id)
+            .execute())
   except Star.DoesNotExist:
     raise DataModelException('Star not found.')
 
-  star.delete_instance()
-
 
 def get_user_starred_repositories(user, limit=None, page=None):
   """ Retrieves all of the repositories a user has starred. """