[errors] Greatly simplify common/errors package.

vpython/venv/prune.go

Index: vpython/venv/prune.go
diff --git a/vpython/venv/prune.go b/vpython/venv/prune.go
index f00004567a62a8f3271856a3a161f65f154eebf9..5a786ec7624af7978e19fdb1b77a55a4969f441b 100644
--- a/vpython/venv/prune.go
+++ b/vpython/venv/prune.go
@@ -84,10 +84,8 @@ func prune(c context.Context, cfg *Config, exempt stringset.Set) error {
 			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