Simplify RipplePublicKey:

This implements the bare minimum necessary to store a 33 byte public
key and use it in ordered containers. It is an efficient and well
defined alternative to RippleAddress when the caller only needs
a node public key.

src/ripple/overlay/impl/PeerImp.cpp

@@ -800,7 +800,7 @@ PeerImp::onMessage (std::shared_ptr <protocol::TMHello> const& m)
         hello_ = *m;
 
         auto const result = overlay_.peerFinder().activate (slot_,
-            RipplePublicKey (publicKey_), cluster);
+            publicKey_.toPublicKey(), cluster);
 
         if (result == PeerFinder::Result::success)
         {