update API doc generate information for cal event
update API doc generate information for cal event

Closes LS-3492

Test Plan: bundle exec rails doc:api generates the calendar events head
documentation correctly.  Go to
http://localhost:3000/doc/api/calendar_events.html (or
canvas.docker/doc...)

Change-Id: Id8e5b6014a5a5e26997769c51145cbde18bc06e8
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/301705
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Davis Hyer <60fbffed049dcae9186e63e354cbc0b825bf5523@instructure.com>
QA-Review: Davis Hyer <60fbffed049dcae9186e63e354cbc0b825bf5523@instructure.com>
Product-Review: Davis Hyer <60fbffed049dcae9186e63e354cbc0b825bf5523@instructure.com>

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