remove AsNoTracking from EngineAssetRepository GetAsset

[JackLewis-digirati]

As part of the work on DeliveryChannels AsNoTracking was added to GetAsset, this is incorrect as by adding AsNoTracking you're fighting against what EF gives you. IIRC we always will update the asset so we definitely do want to track it.

A better solution would be to remove AsNoTracking and also remove code that doesn't update the asset if it's already being tracked, i.e.: https://github.com/dlcs/protagonist/blob/develop/src/protagonist/Engine/Data/EngineAssetRepository.cs#L167-L176

[donaldgray]

Some further context:

The code in https://github.com/dlcs/protagonist/blob/develop/src/protagonist/Engine/Data/EngineAssetRepository.cs#L167-L176 is to handle the fact that the Asset may (when handling Timebased completion, in response to ElasticTranscoder raising completed notification) or may not (when API calls engine directly or via queue) have been loaded from dbContext. Therefor when saving we need to know whether it's tracked, or needs to be attached.

However, #622 changes this behaviour so that the Asset is always loaded from the dbContext regardless of the entrypoint to the engine. Using .AsNoTracking() mimicks the current behaviour (sometimes tracked, sometimes not) but this also means we need to keep the unnecessary complexity of working out whether it's tracked or not.