ProjectExplorer: Simplify BuildStepFactory

De-QObject-ify class, tr contexts are now the product's
context, which was the case in some BuildStepFactories already,
and is current state in {Run,DeployConfiguration}Factory.
One spurious object name removed.

De-virtualize canHandle(), it was never overloaded and is not
intended to be overloaded anymore.

Remove unused clone() function.

Change-Id: Iff7fba5f707505f868f94458084a18650535fa23
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/ios/iosdsymbuildstep.h

@@ -90,7 +90,6 @@ private:
 
 class IosDsymBuildStepFactory : public ProjectExplorer::BuildStepFactory
 {
-    Q_OBJECT
 public:
     explicit IosDsymBuildStepFactory();
 };