[errors] Greatly simplify common/errors package.

luci_config/server/cfgclient/backend/client/client.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 client implements a config client backend for a configuration client.
 package client
 
 import (
         "fmt"
         "net/http"
@@ skipping 57 matching lines @@
 
         svc := be.GetConfigInterface(c, p.Authority)
 
         var fn func(context.Context, string, bool) ([]config.Config, error)
         switch t {
         case backend.GetAllProject:
                 fn = svc.GetProjectConfigs
         case backend.GetAllRef:
                 fn = svc.GetRefConfigs
         default:
-                return nil, errors.Reason("unknown GetAllType: %(type)q").D("type", t).Err()
+                return nil, errors.Reason("unknown GetAllType: %q", t).Err()
         }
 
         cfgs, err := fn(c, path, !p.Content)
         if err != nil || len(cfgs) == 0 {
                 return nil, translateConfigErr(err)
         }
 
         items := make([]*backend.Item, len(cfgs))
         for i := range cfgs {
                 items[i] = makeItem(&cfgs[i])
@@ skipping 101 matching lines @@
         case backend.AsAnonymous:
                 return auth.NoAuth
         case backend.AsService:
                 return auth.AsSelf
         case backend.AsUser:
                 return auth.AsUser
         default:
                 panic(fmt.Errorf("unknown config Authority (%d)", a))
         }
 }