Fix not removed watches on unallowed repositories (#4201)

models/repo_collaboration.go

@@ -172,5 +172,14 @@ func (repo *Repository) DeleteCollaboration(uid int64) (err error) {
 		return err
 	}
 
+	if err = watchRepo(sess, uid, repo.ID, false); err != nil {
+		return err
+	}
+
+	// Remove all IssueWatches a user has subscribed to in the repository
+	if err := removeIssueWatchersByRepoID(sess, uid, repo.ID); err != nil {
+		return err
+	}
+
 	return sess.Commit()
 }