clarify the duplicate

Change-Id: I5d4a64a7d7effc49f982ad33fa6a535d99863f96
Reviewed-on: https://gerrit.libreoffice.org/2404Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>

sd/source/ui/unoidl/unomodel.cxx

@@ -2736,6 +2736,7 @@ void SAL_CALL SdMasterPagesAccess::remove( const uno::Reference< drawing::XDrawP
             rDoc.AddUndo(rDoc.GetSdrUndoFactory().CreateUndoDeletePage(*pPage));
         }
 
+        // remove both pages
         rDoc.RemoveMasterPage( nPage );
         rDoc.RemoveMasterPage( nPage );