svtools: Delete copy ctor in a standard way

Change-Id: I3d44c7b0ff16897b49f3f3e5a7026dcd1be1301f
Reviewed-on: https://gerrit.libreoffice.org/46645Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

include/svtools/grfmgr.hxx

@@ -498,8 +498,8 @@ private:
     sal_uLong               mnUsedSize; // currently used memory footprint of all swapped in graphics
     GraphicCache*           mpCache;
 
-                        GraphicManager( const GraphicManager& ) {}
-    GraphicManager&     operator=( const GraphicManager& ) { return *this; }
+                        GraphicManager( const GraphicManager& ) = delete;
+    GraphicManager&     operator=( const GraphicManager& ) = delete;
 
     bool SVT_DLLPRIVATE ImplDraw(
                             OutputDevice* pOut,