[errors] Greatly simplify common/errors package.

common/errors/walk_test.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 errors
 
 import (
         "errors"
         "fmt"
         "testing"
@@ skipping 48 matching lines @@
                         errors.New("other error"),
                 } {
                         Convey(fmt.Sprintf(`Registers false for %T %v`, err, err), func() {
                                 So(Any(err, filter), ShouldBeFalse)
                         })
                 }
 
                 for _, err := range []error{
                         testErr,
                         MultiError{errors.New("other error"), MultiError{testErr, nil}},
-                        Annotate(testErr).Reason("error test").Err(),
+                        Annotate(testErr, "error test").Err(),
                 } {
                         Convey(fmt.Sprintf(`Registers true for %T %v`, err, err), func() {
                                 So(Any(err, filter), ShouldBeTrue)
                         })
                 }
         })
 }
-
-func TestContains(t *testing.T) {
-        t.Parallel()
-
-        Convey(`Testing the Contains function for a sentinel error`, t, func() {
-                sentinel := errors.New("test error")
-
-                for _, err := range []error{
-                        nil,
-                        errors.New("foo"),
-                        errors.New("test error"),
-                } {
-                        Convey(fmt.Sprintf(`Registers false for %T %v`, err, err), func() {
-                                So(Contains(err, sentinel), ShouldBeFalse)
-                        })
-                }
-
-                for _, err := range []error{
-                        sentinel,
-                        MultiError{errors.New("other error"), MultiError{sentinel, nil}},
-                } {
-                        Convey(fmt.Sprintf(`Registers true for %T %v`, err, err), func() {
-                                So(Contains(err, sentinel), ShouldBeTrue)
-                        })
-                }
-        })
-}