Revert "Update event.html"

This reverts commit d6d878f890b8ba2c125a29fb2393d7003edcd3d6,
as EventKit is a highly implementation specific, and we already
have an implementation agnostic info box below, that points to EventKit
and other event webhook libraries and apps.

Ultimately, after much discussion with other mantainers we decided this
would be a better solution.