ProjectExplorer: Use std::function for SimpleTargetRunner::start()

This spares us the typical r = runnable(); modify(r); setRunnable(r)
roundtrip and the m_runnable storage that might or might not
be the same as runControl->runnable. Similar for m_device.

Change-Id: I8300260dd8dd7cd395e40bcd3d2ae45089085008
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/debuggerplugin.cpp

@@ -1656,7 +1656,6 @@ public:
 
         auto gdbServer = new GdbServerRunner(runControl, portsGatherer());
         gdbServer->setUseMulti(false);
-        gdbServer->setDevice(runControl->device());
         gdbServer->setAttachPid(ProcessHandle(pid));
 
         addStartDependency(gdbServer);