Merge pull request #6373 from murlakatamenka/master

Update mainwindow.h (remove duplicate declaration)

src/gui/mainwindow.h

@@ -51,7 +51,6 @@ class TransferListWidget;
 class TransferListFiltersWidget;
 class PropertiesWidget;
 class StatusBar;
-class about;
 class TorrentCreatorDlg;
 class downloadFromURL;
 class LineEdit;