Remove privatekey: from the protocol specification

[JeremyTubongbanua]

@gkc says privatekey: is obsolete and is never used.

The objective of this ticket is to remove privatekey: documentation from the protocl specification and remove it from any regex patterns.

[JeremyTubongbanua]

@gkc I can pick this up this sprint PR 87

[gkc]

@JeremyTubongbanua sounds good thank you

[JeremyTubongbanua]

@XavierChanth I had a PR on this here : #133

feel free to overwrite or close or whatever to the branch/PR

[XavierChanth]

@XavierChanth I had a PR on this here : #133

feel free to overwrite or close or whatever to the branch/PR

Thanks, I didn't see this until after, but I've ended up with very similar changes + some other changes I was making to other things.