[BEAM-9430] Update CHANGES.md to reflect removal of ProcessContext#updateWatermark

[lukecwik]

---

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Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---		---	---
Java
Python		---			---	---
XLang	---	---	---		---	---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website
Non-portable
Portable	---		---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

[lukecwik]

R: @mxm

Follow up for #10992

[iemejia]

LGTM

[iemejia]

I am not sure if this means now that we can resolve the issue. Please do it yourself if it is the case @lukecwik

[mxm]

Do we plan to add some end-user documentation for WatermarkEstimators or SDF in general?

[lukecwik]

Yes, there should be some examples of how to write SDFs added to our docs.
After Java SDFs have a way to report progress and backlog, then we should be able to do this in Python and Java (and mention that Go is in the works).

Are the docs something you were interested in doing?

[mxm]

Interested yes but unfortunately won't have time to work on that at the moment.

[mxm]

Thanks @lukecwik.

@iemejia Why the quick merge if a review was still pending on me?

[iemejia]

Oh sorry it was just obviously good so I proceeded. Next time I will wait.

[mxm]

If there was nobody assigned I think that would have been fair, but given that less than a day had passed and a review was explicitly requested, I think it is better to wait. There is no need to rush such things.