Valgrind: Remove unused ValgrindRunner::Private:workingDirectory

This is covered now be the debuggee member.

Change-Id: Id2983e2b8d74236249263fdd4b867bd310bf20cc
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>

src/plugins/valgrind/valgrindrunner.cpp

@@ -56,7 +56,6 @@ public:
     QString valgrindExecutable;
     QStringList valgrindArguments;
     StandardRunnable debuggee;
-    QString workingdir;
     bool useStartupProject = true;
     QSsh::SshConnectionParameters connParams;
 };