Valgrind: Make the (threaded) parser a proper member of the runner

Simplifies user code, and it was only ever used in a 1:1 relation,
even in the tests.

Change-Id: I3ce4fc83a361aceb730c05420efdb4ea52d37cda
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/valgrind/memcheckengine.h

@@ -60,7 +60,6 @@ private:
     void startDebugger();
     void appendLog(const QByteArray &data);
 
-    XmlProtocol::ThreadedParser m_parser;
     ValgrindRunner m_runner;
     const bool m_withGdb;
 };