MovieGenre and SearchString aren't used as MovieGenreViewModel properties

It seems `MovieGenre` and `SearchString` properties of `MovieGenreViewModel` are not necessary (used), since we used stand-alone parameters in both action and view.
Did I miss something?

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#### Document Details

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* ID: f9b9859c-b83c-5fc3-41d5-15531232185f
* Version Independent ID: 5438de31-8562-3747-d1a5-2a4622252fc1
* Content: [Add search to an ASP.NET Core MVC app](https://docs.microsoft.com/en-us/aspnet/core/tutorials/first-mvc-app/search?view=aspnetcore-3.1)
* Content Source: [aspnetcore/tutorials/first-mvc-app/search.md](https://github.com/aspnet/AspNetCore.Docs/blob/master/aspnetcore/tutorials/first-mvc-app/search.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-tutorials**
* GitHub Login: @Rick-Anderson
* Microsoft Alias: **riande**