Core: Remove ICore::appMainWindow()

Not seriously needed.

Change-Id: Ide001ce83f9e86306f5d13597716d2ab0d50abbf
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/coreplugin/icore.cpp

@@ -462,11 +462,6 @@ QWidget *ICore::mainWindow()
     return m_mainwindow;
 }
 
-Utils::AppMainWindow *ICore::appMainWindow()
-{
-    return m_mainwindow;
-}
-
 QStatusBar *ICore::statusBar()
 {
     return m_mainwindow->statusBar();