Remove handling of old cases from ServiceFetchAction.eval

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Previously in the 2.1.x release of the Service Fetch the admin UI of the ServiceFetchAction logic action, a ServiceFetchConfiguration was not tied to a User Defined Variable and the action allowed to change the values of both variables and components directly. This has changed with the configuration modal.

ServiceFetchAction.eval() still contains a shim that handles the old case. This should be tackled with a datamigration and/or handled in the serializer/import step.

This change in behaviour should also be documented #2884 , both in the manual and in test cases.