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

net/proxy/proxy_info.h

Index: net/proxy/proxy_info.h
diff --git a/net/proxy/proxy_info.h b/net/proxy/proxy_info.h
index 8d799e28b94873278cee917466d24b47388d2fc7..69c87c8bccd71fcd1d531cf11898f27cf3e4a838 100644
--- a/net/proxy/proxy_info.h
+++ b/net/proxy/proxy_info.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.
 
@@ -13,8 +13,6 @@
 #include "net/proxy/proxy_retry_info.h"
 #include "net/proxy/proxy_server.h"
 
-class GURL;
-
 namespace net {
 
 // This object holds proxy information returned by ResolveProxy.