Debugger: Re-enable breakpoint state handling with keyboard

This patch re-enables disabling or enabling breakpoints using
the respective keyboard shortcut.
Had been disabled since d6911fd10c.

Change-Id: Iea3ce679bafcc78910be07984fd03b4a6e66eb8b
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/breakhandler.h

@@ -98,7 +98,7 @@ private:
     void updateMarker();
     void updateMarkerIcon();
     void destroyMarker();
-    void scheduleSynchronization();
+//    void scheduleSynchronization();
     QPointer<DebuggerEngine> usingEngine() const;
 
     bool isEngineRunning() const;