- #3612 subpart 2 of 2
- merge `ActionConstraintsWebSite`, `AntiforgeryTokenWebSite` and `ContentNegotiationWebSite` into `BasicWebSite`
- remove tests depending on `ErrorReporterMiddleware` in merged sites; not used in `BasicWebSite`
- delete `CompositeViewEngineWebSite`, `Microsoft.AspNet.Mvc.ViewEngines.CompositeViewEngineTest` covers cases
- delete `CorsMiddlewareWebsite`, soon to be in Cors repo (see aspnet/CORS#57)
- remove `SendFileMiddleware` from FilesWebSite, unused there
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