[MDAPI-124] [.NET] Remove the ability to pass multiple sources for PriceLeveBookSample#80

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feature/MDAPI-124-.net-remove-the-ability-to-pass-multiple-sources-for-pricelevebooksampledxFeed/dxfeed-graal-net-api:feature/MDAPI-124-.net-remove-the-ability-to-pass-multiple-sources-for-pricelevebooksampleCopy head branch name to clipboard