debugger: get rid of the private header dependency

Removed the CanvasFrameRate class as it is not used, and
depends on private Qt API

src/plugins/debugger/debuggerrunner.cpp

@@ -370,11 +370,9 @@ void DebuggerRunControl::createEngine(const DebuggerStartParameters &sp)
         case TcfEngineType:
             m_engine = createTcfEngine(sp);
             break;
-#if defined(QML_ENGINE)
         case QmlEngineType:
             m_engine = createQmlEngine(sp);
             break;
-#endif
         default: {
             // Could not find anything suitable.
             debuggingFinished();