toplevel class can't have static

if pasting the code into toplevel class you end up with error so removing it from the client endpoint

(cherry picked from commit 3fcf02e)

docs/src/main/asciidoc/websockets-next-reference.adoc

@@ -819,7 +819,7 @@ Let’s consider the following client endpoint:
 [source, java]
 ----
 @WebSocketClient(path = "/endpoint/{name}")
-public static class ClientEndpoint {
+public class ClientEndpoint {
 
     @OnTextMessage
     void onMessage(@PathParam String name, String message, WebSocketClientConnection connection) {