components: Cleanup class/struct fwd declarations

components/sync/engine_impl/sync_manager_impl.h

Index: components/sync/engine_impl/sync_manager_impl.h
diff --git a/components/sync/engine_impl/sync_manager_impl.h b/components/sync/engine_impl/sync_manager_impl.h
index caf0e5cce3cdc064e3d7b66e4e21e6f73cf286cf..d448c4c15370a5709b757b0eaf2e292057e5a158 100644
--- a/components/sync/engine_impl/sync_manager_impl.h
+++ b/components/sync/engine_impl/sync_manager_impl.h
@@ -33,15 +33,11 @@
 #include "components/sync/syncable/user_share.h"
 #include "net/base/network_change_notifier.h"
 
-class GURL;
-
 namespace syncer {
 
 class ModelTypeRegistry;
 class SyncCycleContext;
 class TypeDebugInfoObserver;
-class WriteNode;
-class WriteTransaction;
 
 // SyncManager encapsulates syncable::Directory and serves as the parent of all
 // other objects in the sync API.  If multiple threads interact with the same