[errors] Greatly simplify common/errors package.

logdog/client/cmd/logdog_butler/subcommand_stream.go

 // Copyright 2015 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 main
 
 import (
         "os"
 
         "github.com/luci/luci-go/common/errors"
@@ skipping 74 matching lines @@
         output, err := of.configOutput(a)
         if err != nil {
                 log.WithError(err).Errorf(a, "Failed to create output instance.")
                 return runtimeErrorReturnCode
         }
         defer output.Close()
 
         // Instantiate our Processor.
         err = a.runWithButler(output, func(b *butler.Butler) error {
                 if err := b.AddStream(streamFile, cmd.stream.properties()); err != nil {
-                        return errors.Annotate(err).Reason("failed to add stream").Err()
+                        return errors.Annotate(err, "failed to add stream").Err()
                 }
 
                 b.Activate()
                 return b.Wait()
         })
         if err != nil {
                 logAnnotatedErr(a, err, "Failed to stream file.")
                 return runtimeErrorReturnCode
         }
 
         return 0
 }