Disable UI if it's not compiled in. (#5773)

* Disable UI if it's not compiled in.

* Properly enabled/disable ui server depending on features.

parity/configuration.rs

@@ -1036,7 +1036,7 @@ impl Configuration {
 			self.args.flag_geth ||
 			self.args.flag_no_ui;
 
-		!ui_disabled
+		!ui_disabled && cfg!(feature = "ui-enabled")
 	}
 
 	fn verifier_settings(&self) -> VerifierSettings {

parity/rpc.rs

@@ -102,7 +102,7 @@ impl From<UiConfiguration> for HttpConfiguration {
 impl Default for UiConfiguration {
 	fn default() -> Self {
 		UiConfiguration {
-			enabled: true,
+			enabled: true && cfg!(feature = "ui-enabled"),
 			port: 8180,
 			interface: "127.0.0.1".into(),
 			hosts: Some(vec![]),