Revert "Shader warm up (#27660)" (#28376)

This reverts commit a44f174efc.

Reason: start_up tests become flaky.

See https://github.com/flutter/flutter/issues/28374

TBR: xster

Merge on red to fix the tree

dev/benchmarks/macrobenchmarks/lib/common.dart

@@ -1,6 +1 @@
-// 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.
-
 const String kCullOpacityRouteName = '/cull_opacity';
-const String kCubicBezierRouteName = '/cubic_bezier';