perf-stream-locked-section: fix the call to the v3 generator

That generator simply return chunks so we should not assign the return to a
tuple.

contrib/perf.py

@@ -2058,8 +2058,7 b' def _find_stream_generator(version):'
     if generatev3 is not None:
 
         def generate(repo):
-            entries, bytes, data = generatev3(repo, None, None, True)
-            return data
+            return generatev3(repo, None, None, True)
 
         available[b'v3-exp'] = generate