[errors] de-specialize Transient in favor of Tags.

common/retry/wrap.go

Index: common/retry/wrap.go
diff --git a/common/retry/wrap.go b/common/retry/wrap.go
deleted file mode 100644
index 7056199fb777ccf805e269d6b1af830e8dfaab7e..0000000000000000000000000000000000000000
--- a/common/retry/wrap.go
+++ /dev/null
@@ -1,17 +0,0 @@
-// 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 retry
-
-// wrap wraps a Factory, applying a modification function to each Iterator
-// that it produces.
-func wrap(g Factory, mod func(it Iterator) Iterator) Factory {
-	return func() Iterator {
-		next := g()
-		if next == nil {
-			return nil
-		}
-		return mod(next)
-	}
-}