Remove special code path for fullscreen support on Mac

This was necessary for supporting full screen on 10.7 even while
keeping compatibility with 10.6. Since we no longer support 10.6,
we can remove the workaround.

Change-Id: I03e23e9203836ab6fb5a836fc06a525e44516d34
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/plugins/coreplugin/mainwindow.h

@@ -107,7 +107,7 @@ public:
 
     void setOverrideColor(const QColor &color);
 
-    void setIsFullScreen(bool fullScreen);
+    void updateFullScreenAction();
 
     bool isNewItemDialogRunning() const;
 
@@ -119,7 +119,7 @@ public slots:
     void newFile();
     void openFileWith();
     void exit();
-    void setFullScreen(bool on);
+    void toggleFullScreen();
 
     void showNewItemDialog(const QString &title,
                            const QList<IWizardFactory *> &factories,