TaskTree: Get rid of registration macros

Alias task types manually.
Don't require the alias to be inside the Tasking namespace.
Addresses the 22th point of the jira ticket below.

Task-number: QTCREATORBUG-28741
Change-Id: I1bdda7fe5a01e4bcb5052ec328f4e0eace878651
Reviewed-by: hjk <hjk@qt.io>

src/plugins/ios/iosdeploystep.cpp

@@ -97,11 +97,7 @@ private:
     void start() final { task()->start(); }
 };
 
-} // Ios::Internal
-
-TASKING_DECLARE_TASK(IosTransferTask, Ios::Internal::IosTransferTaskAdapter);
-
-namespace Ios::Internal {
+using IosTransferTask = CustomTask<IosTransferTaskAdapter>;
 
 class IosDeployStep final : public BuildStep
 {