Delete album from Photos.app
Photos doesn't use Events. Though it imports old ones from iPhoto, it considers them now to be Albums &amp;  won't create new Events of its own.

To delete one, enable the sidebar - View menu or  Cmd ⌘   Opt ⌥   S 
Right click the 'event' &amp; select Delete Album.

This does not delete the photos in it, just the 'container' event.

Installing Photos shouldn't necessarily delete iPhoto. I still have both on my machines, though I did download Photos specifically, as opposed to it being delivered as part of an update. Maybe that changes the behaviour, I'm not sure.