docs: use MyServiceSettings and getStubSettingsBuilder in example

Author: jinseopkim0

OBSERVABILITY.md

@@ -107,11 +107,8 @@ If you need to disable tracing or provide a custom `ApiTracerFactory`, configure
 ```java
 import com.google.api.gax.tracing.NoopApiTracerFactory;
 
-// Example disabling tracing via StubSettings or ClientSettings builder
-MyServiceStubSettings.Builder stubSettingsBuilder = MyServiceStubSettings.newBuilder();
-stubSettingsBuilder.setTracerFactory(NoopApiTracerFactory.getInstance());
-
-MyServiceClientSettings settings = MyServiceClientSettings.newBuilder()
-    .setStubSettings(stubSettingsBuilder)
-    .build();
+// Example disabling tracing via ServiceSettings builder
+MyServiceSettings.Builder settingsBuilder = MyServiceSettings.newBuilder();
+settingsBuilder.getStubSettingsBuilder().setTracerFactory(NoopApiTracerFactory.getInstance());
+MyServiceSettings settings = settingsBuilder.build();
 ```