Remove obsolete role attributes for tab groups in the reference manual

Since we now use asciidoctor-tabs instead of spring-asciidoctor-backends,
we no longer need the `role="primary"` and `role="secondary"` attributes
for tab groups.

Closes gh-33506

framework-docs/modules/ROOT/pages/web/webflux-webclient/client-attributes.adoc

@@ -9,7 +9,7 @@ For example:
 ======
 Java::
 +
-[source,java,indent=0,subs="verbatim,quotes",role="primary"]
+[source,java,indent=0,subs="verbatim,quotes"]
 ----
 	WebClient client = WebClient.builder()
 			.filter((request, next) -> {
@@ -28,7 +28,7 @@ Java::
 
 Kotlin::
 +
-[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
+[source,kotlin,indent=0,subs="verbatim,quotes"]
 ----
 	val client = WebClient.builder()
 			.filter { request, _ ->