Replace RE2 import with a dependency

third_party/re2/util/flags.h

-// 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.
-
-// Simplified version of Google's command line flags.
-// Does not support parsing the command line.
-// If you want to do that, see
-// https://gflags.github.io/gflags/
-
-#ifndef RE2_UTIL_FLAGS_H__
-#define RE2_UTIL_FLAGS_H__
-
-#define DEFINE_flag(type, name, deflt, desc) \
-        namespace re2 { type FLAGS_##name = deflt; }
-
-#define DECLARE_flag(type, name) \
-        namespace re2 { extern type FLAGS_##name; }
-
-#define DEFINE_bool(name, deflt, desc) DEFINE_flag(bool, name, deflt, desc)
-#define DEFINE_int32(name, deflt, desc) DEFINE_flag(int32, name, deflt, desc)
-#define DEFINE_string(name, deflt, desc) DEFINE_flag(string, name, deflt, desc)
-
-#define DECLARE_bool(name) DECLARE_flag(bool, name)
-#define DECLARE_int32(name) DECLARE_flag(int32, name)
-#define DECLARE_string(name) DECLARE_flag(string, name)
-
-#endif  // RE2_UTIL_FLAGS_H__