Remove code when Roslyn fixed the bug

[lsoft]

We need to remove this list filtering:

//RoslynDocumentHelper.GetDocumentByDocumentIdAsync

            document = (await project.GetSourceGeneratedDocumentsAsync(CancellationToken.None))
                .First(d => d.Id.Equals(documentId));

and just use project.GetSourceGeneratedDocumentAsync.

Tracking issue: dotnet/roslyn#71581