Remove some premature optimisation

Reduces header dependencies.
diff --git a/vncviewer/CConn.cxx b/vncviewer/CConn.cxx
index cf963f0..c5cd4a4 100644
--- a/vncviewer/CConn.cxx
+++ b/vncviewer/CConn.cxx
@@ -44,6 +44,7 @@
 
 #include "CConn.h"
 #include "OptionsDialog.h"
+#include "DesktopWindow.h"
 #include "i18n.h"
 #include "parameters.h"
 #include "vncviewer.h"