[test] Remove deprecated GraphTester helper class.

test/cctest/compiler/graph-tester.h

-// Copyright 2014 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef V8_CCTEST_COMPILER_GRAPH_TESTER_H_
-#define V8_CCTEST_COMPILER_GRAPH_TESTER_H_
-
-#include "src/v8.h"
-#include "test/cctest/cctest.h"
-
-#include "src/compiler/common-operator.h"
-#include "src/compiler/graph.h"
-
-namespace v8 {
-namespace internal {
-namespace compiler {
-
-class GraphTester : public HandleAndZoneScope, public Graph {
- public:
-  GraphTester() : Graph(main_zone()) {}
-};
-
-}  // namespace compiler
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_CCTEST_COMPILER_GRAPH_TESTER_H_