[errors] Greatly simplify common/errors package.

vpython/venv/prune.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 venv
 
 import (
         "github.com/danjacques/gofslock/fslock"
         "golang.org/x/net/context"
 
@@ skipping 66 matching lines @@
                         if cfg.MaxPrunesPerSweep > 0 && totalPruned >= cfg.MaxPrunesPerSweep {
                                 logging.Debugf(c, "Hit prune limit of %d.", cfg.MaxPrunesPerSweep)
                                 hitLimitStr = " (limit)"
                                 cancelFunc()
                         }
 
                 case fslock.ErrLockHeld:
                         logging.WithError(err).Debugf(c, "Environment [%s] is in use.", e.Name)
 
                 default:
-                        err = errors.Annotate(err).Reason("failed to prune file: %(name)s").
-                                D("name", e.Name).
-                                D("dir", e.Config.BaseDir).
-                                Err()
+                        err = errors.Annotate(err, "failed to prune file: %s", e.Name).
+                                InternalReason("dir(%q)", e.Config.BaseDir).Err()
                         allErrs = append(allErrs, err)
                 }
                 return nil
         })
         if err != nil {
                 // Error during iteration.
                 return err
         }
 
         logging.Infof(c, "Pruned %d environment(s)%s with %d error(s)", totalPruned, hitLimitStr, len(allErrs))
         if len(allErrs) > 0 {
                 return allErrs
         }
         return nil
 }