I feel pretty dumb asking this but… 
How do you delete extra note columns in a track? I tried ‘Cut’ but that doesn’t do what I want.
Hey
Not a dumb question if it isn’t immediately apparent what to do.
At the top of the track, on the pattern editor, you will see small ‘-’ button.
Click this.
Ahh yes the one that sits on the top left! Thanks 
The hotkey for expanding/collapsing columns is ctrl-shift-left/ctrl-shift-right, incidentally.