message: Mention ISummarizerRuntime deprecated methods
  [How contribute to this
  repo](https://github.com/microsoft/FluidFramework/blob/main/CONTRIBUTING.md).
  [Guidelines for Pull
  Requests](https://github.com/microsoft/FluidFramework/wiki/PR-Guidelines#guidelines).
  ## Description
  These APIs were deprecated in
  [#9957](https://github.com/microsoft/FluidFramework/pull/9957) but
  weren't mentioned in BREAKING.md
diff: @@ -15,6 +15,17 @@ It's important to communicate breaking changes to our stakeholders. To write a g
  - Avoid using code formatting in the title (it's fine to use in the body).
  - To explain the benefit of your change, use the [What's New](https://fluidframework.com/docs/updates/v1.0.0/) section on FluidFramework.com.
  +# 2.0.0-internal.2.1.0
  +
  +## 2.0.0-internal.2.1.0 Upcoming changes
  +- [Deprecated ISummarizerRuntime batchEnd listener](#Deprecated-ISummarizerRuntime-batchEnd-listener)
  +
  +### Deprecated ISummarizerRuntime batchEnd listener
  +The `"batchEnd"` listener in `ISummarizerRuntime` has been deprecated and will be removed in a future release. Please remove all usage and implementations of `ISummarizerRuntime.on("batchEnd", ...)` and `ISummarizerRuntime.removeListener("batchEnd", ...)`.
  +If these methods are needed, please refer to the `IContainerRuntimeBase` interface.
  +
  +## 2.0.0-internal.2.1.0 Breaking changes
  +
  # 2.0.0-internal.2.0.0
  ## 2.0.0-internal.2.0.0 Upcoming changes
  