remove deprecated annotation from Metadata.pubKeyCS

[gkc]

Is your feature request related to a problem? Please describe.

pubKeyCS is marked as deprecated but support for pubKeyHash (the proposed replacement) has not yet been added to at_server or at_client_sdk

Describe the solution you'd like

I think to prevent confusion we need to remove the deprecation annotation until at_server and at_client_sdk fully support pubKeyHash.

Additional context

While I was on a lint cleanup spree in at_secondary_server, I noticed that while there were lint info messages regarding pubKeyCS being deprecated, there was no mention of pubKeyHash anywhere in the at_server codebase, nor any of the other atsign-foundation repos. The annotation description, "use pubKeyHash" is therefore, currently, both misleading and bad advice.