Replace RE2 import with a dependency

third_party/re2/util/thread.h

Index: third_party/re2/util/thread.h
diff --git a/third_party/re2/util/thread.h b/third_party/re2/util/thread.h
deleted file mode 100644
index fb67bdc6de629350a3f95e3f70390167be821bbc..0000000000000000000000000000000000000000
--- a/third_party/re2/util/thread.h
+++ /dev/null
@@ -1,33 +0,0 @@
-// Copyright 2009 The RE2 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 RE2_UTIL_THREAD_H__
-#define RE2_UTIL_THREAD_H__
-
-#ifdef _WIN32
-#include <windows.h>
-#else
-#include <pthread.h>
-#endif
-
-class Thread {
- public:
-  Thread();
-  virtual ~Thread();
-  void Start();
-  void Join();
-  void SetJoinable(bool);
-  virtual void Run() = 0;
-
- private:
-#ifdef _WIN32
-  HANDLE pid_;
-#else
-  pthread_t pid_;
-#endif
-  bool running_;
-  bool joinable_;
-};
-
-#endif  // RE2_UTIL_THREAD_H__