Remove obviously unneeded forward declarations from headers under src/{app,base,net}.

base/file_version_info_mac.h

Index: base/file_version_info_mac.h
diff --git a/base/file_version_info_mac.h b/base/file_version_info_mac.h
index 6f94baa37b11b18282bf6bd03fd8c31c03d483cb..d66c4e6343c7b316eb6263c628d87712c2353b7d 100644
--- a/base/file_version_info_mac.h
+++ b/base/file_version_info_mac.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 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.
 
@@ -18,8 +18,6 @@
 class NSBundle;
 #endif
 
-class FilePath;
-
 // Provides a way to access the version information for a file.
 // This is the information you access when you select a file in the Windows
 // explorer, right-click select Properties, then click the Version tab.