config_builder+rpcwallet: simplify RPC signing

With the remote signing instance now not needing to know anything about
addresses or current derivation indices, we don't need to forward any
such calls to that instance and can simplify the RPCKeyRing
considerably.

config_builder.go

@@ -687,7 +687,7 @@ func (d *RPCSignerWalletImpl) BuildChainControl(
 
 	rpcKeyRing, err := rpcwallet.NewRPCKeyRing(
 		baseKeyRing, walletController,
-		d.DefaultWalletImpl.cfg.RemoteSigner,
+		d.DefaultWalletImpl.cfg.RemoteSigner, walletConfig.CoinType,
 		rpcwallet.DefaultRPCTimeout,
 	)
 	if err != nil {