Change default for streaming feature flag to false (#6310)

Author: verult

cirq-google/cirq_google/engine/engine.py

@@ -89,7 +89,7 @@ def __init__(
         timeout: Optional[int] = None,
         serializer: Serializer = CIRCUIT_SERIALIZER,
         # TODO(#5996) Remove enable_streaming once the feature is stable.
-        enable_streaming: bool = True,
+        enable_streaming: bool = False,
     ) -> None:
         """Context and client for using Quantum Engine.