Update sample city file for devopsdays-theme

[mattstratton]

Update yyyy-city.yml with any new fields, and remove any that are no longer needed

List of fields to add (this will be a work in progress)

• event_logo_square: 'logo-square.jpg'
• event_logo: 'logo.jpg'
• event_twitter: 'devopsdays (without the @ sign)
• registration_open: 'false'
• registration_link: "" (this is an optional link if they want off-site registration)
• cfp_open: "false"
• cfp_link: ""

[mattstratton]

@mattstratton will provide a list in this ticket of fields to change.

[bridgetkromhout]

I already removed fields like friendly: that aren't used anymore. I added these ones in the utilities dir over in the theme repo, and updating the utilities dir in this repo is on the release checklist.