fix shutdown paths

this includes:
- move the gdb ownership back to the engine (thus strip down the
  adaptors as far as possible)
- make gdb startup synchronous
- make adapter shutdown synchronous
- fix the state transitions relating to shutdown

src/plugins/debugger/gdb/remotegdbadapter.h

@@ -69,12 +69,6 @@ private:
 #endif
     void handleFileExecAndSymbols(const GdbResponse &response);
     void handleTargetRemote(const GdbResponse &response);
-    void handleKill(const GdbResponse &response);
-    void handleExit(const GdbResponse &response);
-
-    Q_SLOT void handleGdbStarted();
-    Q_SLOT void handleGdbError(QProcess::ProcessError error);
-    Q_SLOT void handleGdbFinished(int, QProcess::ExitStatus);
 
     QProcess m_uploadProc;
 };