doc: add emitter.off to events.md
emitter.off is not listed in the current document. This patch adds that to the events.md.
Refs: #17156
Checklist
-
documentation is changed or added -
commit message follows commit guidelines
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
emitter.off is not listed in the current document. This patch adds that to the events.md.
Refs: #17156