[errors] Greatly simplify common/errors package.

milo/build_source/raw_presentation/html.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package raw_presentation
 
 import (
         "net/http"
         "strings"
 
@@ skipping 69 matching lines @@
 }
 
 func resolveHost(host string) (string, error) {
         // Resolveour our Host, and validate it against a host whitelist.
         switch host {
         case "":
                 return defaultLogDogHost, nil
         case defaultLogDogHost, "luci-logdog-dev.appspot.com":
                 return host, nil
         default:
-                return "", errors.Reason("host %(host)q is not whitelisted").
-                        D("host", host).
-                        Err()
+                return "", errors.Reason("host %q is not whitelisted", host).Err()
         }
 }
 
 // NewClient generates a new LogDog client that issues requests on behalf of the
 // current user.
 func NewClient(c context.Context, host string) (*coordinator.Client, error) {
         var err error
         if host, err = resolveHost(host); err != nil {
                 return nil, err
         }
 
         // Initialize the LogDog client authentication.
         t, err := auth.GetRPCTransport(c, auth.AsUser)
         if err != nil {
                 return nil, errors.New("failed to get transport for LogDog server")
         }
 
         // Setup our LogDog client.
         return coordinator.NewClient(&prpc.Client{
                 C: &http.Client{
                         Transport: t,
                 },
                 Host: host,
         }), nil
 }