refactor(e2e): remove unused useMessagesStreamHelper parameter

Now that auto-hook instrumentation also uses client.messages.stream(),
the useMessagesStreamHelper flag is always true and the fallback branch
is unreachable. Remove the parameter and simplify the stream-with-response
operation to unconditionally use client.messages.stream().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Qard

e2e/scenarios/anthropic-instrumentation/scenario.impl.mjs

@@ -26,11 +26,7 @@ const WEATHER_TOOL = {
 
 async function runAnthropicInstrumentationScenario(
   Anthropic,
-  {
-    decorateClient,
-    useBetaMessages = true,
-    useMessagesStreamHelper = true,
-  } = {},
+  { decorateClient, useBetaMessages = true } = {},
 ) {
   const imageBase64 = (
     await readFile(new URL("./test-image.png", import.meta.url))
@@ -123,33 +119,18 @@ async function runAnthropicInstrumentationScenario(
         "anthropic-stream-with-response-operation",
         "stream-with-response",
         async () => {
-          const stream =
-            useMessagesStreamHelper === false
-              ? await client.messages.create({
-                  model: ANTHROPIC_MODEL,
-                  max_tokens: 32,
-                  temperature: 0,
-                  stream: true,
-                  messages: [
-                    {
-                      role: "user",
-                      content:
-                        "Count from 1 to 3 and include the words one two three.",
-                    },
-                  ],
-                })
-              : client.messages.stream({
-                  model: ANTHROPIC_MODEL,
-                  max_tokens: 32,
-                  temperature: 0,
-                  messages: [
-                    {
-                      role: "user",
-                      content:
-                        "Count from 1 to 3 and include the words one two three.",
-                    },
-                  ],
-                });
+          const stream = client.messages.stream({
+            model: ANTHROPIC_MODEL,
+            max_tokens: 32,
+            temperature: 0,
+            messages: [
+              {
+                role: "user",
+                content:
+                  "Count from 1 to 3 and include the words one two three.",
+              },
+            ],
+          });
           await collectAsync(stream);
         },
       );