QmlProfiler: Disconnect some signals on shutdown

It's a workaround, not a proper solution (as indicated by the
SOFT ASSERT: "d->m_profilerState" in file qmlprofilerruncontrol.cpp,
line 144 triggering) The state manager (and possibly more)
is referenced from potentially running run controls, that are ramped
down after the plugin.

Task-number: QTCREATORBUG-18736
Change-Id: Ia20b168fe640c818276a777e1d23feab0cacd565
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/plugins/qmlprofiler/qmlprofilerplugin.cpp

@@ -89,7 +89,7 @@ bool QmlProfilerPlugin::initialize(const QStringList &arguments, QString *errorS
 
 void QmlProfilerPlugin::extensionsInitialized()
 {
-    (void) new QmlProfilerTool(this);
+    m_profilerTool = new QmlProfilerTool(this);
 
     addAutoReleasedObject(new QmlProfilerOptionsPage);
 
@@ -111,6 +111,8 @@ void QmlProfilerPlugin::extensionsInitialized()
 
 ExtensionSystem::IPlugin::ShutdownFlag QmlProfilerPlugin::aboutToShutdown()
 {
+    delete m_profilerTool;
+
     // Save settings.
     // Disconnect from signals that are not needed during shutdown
     // Hide UI (if you add UI that is not in the main window directly)