[anonsec] Propose dropping asymmetric CBB

[Joe Touch]

Should it be included as a variant for completeness, but the lack of
currently known utility / motivation noted?

Sam Hartman wrote:
> 
> I propose that we drop the applicability statement for asymmetric CBB because I don't think it is useful.
> 
> I think the other applicability statements are much better than in
> previous versions.
> 
> --Sam
> 
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