[errors] Greatly simplify common/errors package.

logdog/client/butlerlib/streamclient/tcp.go

 // Copyright 2017 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 streamclient
 
 import (
         "io"
         "net"
 
         "github.com/luci/luci-go/common/errors"
 )
 
 func tcpProtocolClientFactory(netType string) ClientFactory {
         return func(spec string) (Client, error) {
                 raddr, err := net.ResolveTCPAddr(netType, spec)
                 if err != nil {
-                        return nil, errors.Annotate(err).Reason("could not resolve %(net)q address from %(spec)q").
-                                D("net", netType).
-                                D("spec", spec).
-                                Err()
+                        return nil, errors.Annotate(err, "could not resolve %q address from %q", netType, spec).Err()
                 }
 
                 if raddr.IP == nil || raddr.IP.IsUnspecified() {
-                        return nil, errors.Reason("a valid %(net)q address must be provided").
-                                D("net", netType).
-                                Err()
+                        return nil, errors.Reason("a valid %q address must be provided", netType).Err()
                 }
 
                 if raddr.Port <= 0 {
                         return nil, errors.New("a valid port must be provided")
                 }
 
                 return &clientImpl{
                         factory: func() (io.WriteCloser, error) {
                                 conn, err := net.DialTCP(netType, nil, raddr)
                                 if err != nil {
-                                        return nil, errors.Annotate(err).Reason("failed to dial %(net)q address %(raddr)q").
-                                                D("net", netType).
-                                                D("raddr", raddr).
-                                                Err()
+                                        return nil, errors.Annotate(err, "failed to dial %q address %q", netType, raddr).Err()
                                 }
                                 return conn, nil
                         },
                 }, nil
         }
 }