Closed Date Editor Documentation Update

[Jessica Woolford]

I have noticed that this outdated page on the Closed Date Editor still comes up when searching the docs:

https://docs.evergreen-ils.org/docs/latest/admin/closed_dates.html

However, the navigation tree on the left only shows documentation on the Emergency Closed Date Handler:

https://docs.evergreen-ils.org/docs/latest/admin/emergency_closing_handler.html

I propose that we

1) Remove the outdated page in the first link.
2) Update the Emergency Closing Handler page to include information on entering basic non-emergency closed dates.

I am happy to do this work, but wanted to get opinions from DIG on this approach before I start.