Remove ephelper and other endpoints code.

appengine/ephelper/errors.go

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-package ephelper
-
-import (
-        "github.com/GoogleCloudPlatform/go-endpoints/endpoints"
-)
-
-// StripError converts the supplied error into an endpoints.APIError.
-//
-// If the error is not already an endpoints.APIError, InternalServerError
-// will be returned.
-func StripError(err error) *endpoints.APIError {
-        if err == nil {
-                return nil
-        }
-
-        epErr, ok := err.(*endpoints.APIError)
-        if !ok {
-                epErr = endpoints.InternalServerError.(*endpoints.APIError)
-        }
-        return epErr
-}