CPaster: Clean forward declaration

Change-Id: I05126edb499cff64bd83839933ad831d9845e0e3
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cpaster/cpasterplugin.h

@@ -37,8 +37,6 @@ class QAction;
 QT_END_NAMESPACE
 
 namespace CodePaster {
-class CustomFetcher;
-class CustomPoster;
 class Settings;
 class Protocol;