Remove libs/clock in favor of luci-go/common/clock.

go/src/infra/libs/clock/testclock/context.go

Index: go/src/infra/libs/clock/testclock/context.go
diff --git a/go/src/infra/libs/clock/testclock/context.go b/go/src/infra/libs/clock/testclock/context.go
deleted file mode 100644
index 9ea91fc2e30459cb27942831e7cc38f5732929ef..0000000000000000000000000000000000000000
--- a/go/src/infra/libs/clock/testclock/context.go
+++ /dev/null
@@ -1,20 +0,0 @@
-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-package testclock
-
-import (
-	"time"
-
-	"golang.org/x/net/context"
-	"infra/libs/clock"
-)
-
-// UseTime instantiates a TestClock and returns a Context that is configured to
-// use that clock, as well as the instantiated clock.
-func UseTime(ctx context.Context, now time.Time) (rctx context.Context, tc TestClock) {
-	tc = New(now)
-	rctx = clock.Set(ctx, tc)
-	return
-}