iOS: Use a constant from iosconstant.h as deploy step id

Not really a big win here, but in line with what most others do.

Change-Id: I19f100084c8ca4cc7d0de97125efdc519bdfc972
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/ios/iosdeploystep.h

@@ -34,8 +34,6 @@ class IosDeployStepFactory final : public ProjectExplorer::BuildStepFactory
 {
 public:
     IosDeployStepFactory();
-
-    static Utils::Id stepId();
 };
 
 } // namespace Internal