Remove JSON web signatures securing mechanism

[David-Chadwick]

The description of this security mechanism is that it has now been withdrawn. So shouldn't we also remove it from the directory?

I guess the higher level discussion that the WG needs to have, is what shoud the directory contain. Currently the Introduction states "unofficial directory for all known Verifiable Credential specifications". But does this mean all known usable or active specifications, or all known historical, superceded, and withdrawn specifications?