Cleanup: Remove unused variables in chrome/ found by Scythe.

chrome/utility/image_writer/error_messages.cc

 // Copyright 2014 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.
 
 #include "chrome/utility/image_writer/error_messages.h"
 
 namespace image_writer {
 namespace error {
 
-const char kCleanUp[] = "Failed to clean up after write operation.";
-const char kCloseDevice[] = "Failed to close usb device.";
-const char kCloseImage[] = "Failed to close image file.";
 const char kInvalidDevice[] = "Invalid device path.";
-const char kNoOperationInProgress[] = "No operation in progress.";
 const char kOpenDevice[] = "Failed to open device.";
 const char kOpenImage[] = "Failed to open image.";
 const char kOperationAlreadyInProgress[] = "Operation already in progress.";
 const char kReadDevice[] = "Failed to read device.";
 const char kReadImage[] = "Failed to read image.";
 const char kWriteImage[] = "Writing image to device failed.";
+#if defined(OS_MACOSX)
 const char kUnmountVolumes[] = "Unable to unmount the device.";
+#endif
 const char kVerificationFailed[] = "Verification failed.";
 
 }  // namespace error
 }  // namespace image_writer