remove reference to deleted empty cmd, fix commands output

- Removed a few lingering references to `duckpan empty`
- help text from `duckpan` wasn't showing for me, now it does, but the indenting is weird and for some reason I can't get it to lineup.
    - The commands need to be indented so the parser respects the extra white-space and newlines, but that forces it to indent. For now let's just leave it as is.

// @mwmiller