Debugger: Normalize some state handling

Remove some now-unusual connection to RunControl::finished
and use a finished() callback in the ToolRunner implementation
instead.

Change-Id: Ieddf05a2258d9a300ac50a739d77d9cfaee10ca6
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/debuggerruncontrol.h

@@ -64,8 +64,7 @@ public:
     void start() override;
     void stop() override;
     void onTargetFailure() override;
-
-    void handleFinished();
+    void onFinished() override;
 
     void startFailed();
     void notifyEngineRemoteServerRunning(const QByteArray &msg, int pid);