* remove event pooling and SyntheticEvent#persist from documents
Syntheticevent#event exists in v17, but it does nothing at the version
* add a page for legacy event pooling for _redirects
* add a warning e.persist() is no longer pooled
* Update legacy-event-pooling.md
* docs: update a redirect link for event pooling
* Update legacy-event-pooling.md
* Update legacy-event-pooling.md
* Update reference-events.md
Co-authored-by: Dan Abramov <dan.abramov@gmail.com>