Feedback: Changefeed Message Envelope

Page: https://cockroachlabs.com/docs/v26.1/changefeed-message-envelopes.html

## What is the reason for your feedback?

[ ] Missing the information I need

[ ] Too complicated

[ ] Out of date

[X] Something is broken

[ ] Other

## Additional details

In https://www.cockroachlabs.com/docs/stable/changefeed-message-envelopes#source, `ts_hlc` and `ts_ns` are listed with the same definition. As `ts_ns` has its own section below, I think the first definition just needs to be removed.

Jira issue: DOC-16236