ExtensionSystem: Remove Qt4 support

Remove usage of the Q_EXPORT_PLUGIN macros, which do not exist in Qt 5.

Change-Id: I678c3cf10b9c5d5c1b9f252b0ecd1c97dc810a47
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Christian Stenger <christian.stenger@digia.com>

src/plugins/bazaar/bazaarplugin.cpp

@@ -784,5 +784,3 @@ void BazaarPlugin::updateActions(VcsBase::VcsBasePlugin::ActionState as)
 
 } // namespace Internal
 } // namespace Bazaar
-
-Q_EXPORT_PLUGIN(Bazaar::Internal::BazaarPlugin)