Remove agent string

The agent string was inspired by the HTTP User-Agent header to serve as
a way to identify what's connecting to the cluster.  While there may
have been vision of other software connecting to a controller than the
Clusterio provided ones this seems highly unlikely to ever happen.

Remove redundant agent string for now.

packages/host/host.ts

@@ -51,7 +51,6 @@ export class HostConnector extends lib.WebSocketClientConnector {
 			new lib.MessageRegisterHost(
 				new lib.RegisterHostData(
 					this.hostConfig.get("host.controller_token"),
-					"Clusterio Host",
 					version,
 					this.hostConfig.get("host.name"),
 					this.hostConfig.get("host.id"),