Remove Stellar(Get)PublicKey

[tsusanka]

Remove StellarGetPublicKey and StellarPublicKey messages? The sign/verify functions were removed so I'm not sure we want to keep this

[tsusanka]

@zulucrypto is that okay for you? The pubkey is not used anywhere now, so I think it's better when we remove it. In case the sign/verify functions return, we'll restore this as well

[zulucrypto]

I was planning on using this method when I implemented support for the account viewer so I think it's still necessary.

Usually people only have one Stellar address that they use multiple times, so this method is important to allow people to get their public address that they can share with others.

[tsusanka]

I'm confused. Isn't that what's GetAddress for? Which we plan to keep

[zulucrypto]

Oops, my mistake, I forgot they were separate! Yes, getPublicKey can be removed.

[tsusanka]

Removed in 4305c1d