QmlProfiler: Reset the zoom control only when we're finished loading

Drop the timeChanged signal of QmlProfilerTraceTime, too, as that
doesn't serve a purpose anymore. We don't want intermittent changes
of the trace time to be reflected in the UI when loading.

Change-Id: I85f18b90fc404ec254c68625104d3e3f9077a1d9
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>

src/plugins/qmlprofiler/qmlprofilermodelmanager.h

@@ -51,9 +51,6 @@ public:
     qint64 endTime() const;
     qint64 duration() const;
 
-signals:
-    void timeChanged(qint64,qint64);
-
 public slots:
     void clear();