Debugger: Dont pass DebuggerEngine::State around in a reference

It's an enum, so it doesn't gain anything to pass it by reference.
Anyhow, most slots didn't use const & in the first place ...

Change-Id: I605178092167a455db73dd6773725763b361b4d0
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/debugger/debuggerengine.h

@@ -289,7 +289,7 @@ public:
     QString toFileInProject(const QUrl &fileUrl);
 
 signals:
-    void stateChanged(const Debugger::DebuggerState &state);
+    void stateChanged(Debugger::DebuggerState state);
     // A new stack frame is on display including locals.
     void stackFrameCompleted();
     /*