Remove some unused files

webrtc/rtc_base/system/unused.h

@@ -1,28 +0,0 @@
-/*
- *  Copyright (c) 2018 The WebRTC 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 in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#ifndef RTC_BASE_SYSTEM_UNUSED_H_
-#define RTC_BASE_SYSTEM_UNUSED_H_
-
-// Prevent the compiler from warning about an unused variable. For example:
-//   int result = DoSomething();
-//   RTC_DCHECK(result == 17);
-//   RTC_UNUSED(result);
-// Note: In most cases it is better to remove the unused variable rather than
-// suppressing the compiler warning.
-#ifndef RTC_UNUSED
-#ifdef __cplusplus
-#define RTC_UNUSED(x) static_cast<void>(x)
-#else
-#define RTC_UNUSED(x) (void)(x)
-#endif
-#endif  // RTC_UNUSED
-
-#endif  // RTC_BASE_SYSTEM_UNUSED_H_