Remove unneeded hierarchy from WidgetResizeHandler

A single one is enough

src/WidgetResizeHandler.cpp

@@ -1,31 +0,0 @@
-/*
-  This file is part of KDDockWidgets.
-
-  Copyright (C) 2018-2019 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com
-  Author: Sérgio Martins <sergio.martins@kdab.com>
-
-  This program is free software; you can redistribute it and/or modify
-  it under the terms of the GNU General Public License as published by
-  the Free Software Foundation, either version 2 of the License, or
-  (at your option) any later version.
-
-  This program is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public License
-  along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*/
-
-#include "WidgetResizeHandler_p.h"
-
-#include <QWindow>
-#include <QWidget>
-
-using namespace KDDockWidgets;
-WidgetResizeHandler::WidgetResizeHandler(QWidget *target)
-    : WidgetResizeHandlerBase(target)
-{
-    setTarget(target);
-}