… How does one turn this off? …

Turn off what?

The display or the playback?

What is the problem you are trying to solve?

The better we understand, the better we can help.

You can set Human Playback to ‘None’.

This is done in the Playback Controls.

https://makemusic.zendesk.com/hc/en-us/community/posts/215729367-General-Discussion-House-Rules 

You can also post screen shots, jpeg or png so that we can have an idea of what you are seeing.

Here is what I am talking about, and let me preface this by saying I know how to turn human playback on and off, and I know how to display/not-display hidden notes.  When I playback anything that is a percussion roll, these notes are added.  I am asking how to prevent this from happening.  I have other files where this does not occur, so I am not sure why on this particular file it is.  It is only happening on notes with the 3 slash roll articulation.  This creates editing problems as the "hidden" notes are now counted in speedy entry, and it makes changing things slow and tedious.  

In the View menu, turn off Show Hidden Notes and Rests.

and to batch delete them all?

… and to batch delete them all? …

You are talking about percussion rolls - right?

This way works for me:

MIDI Tool.

MIDI Tool menu > Apply Human Playback…

In the window Apply Human Playback, de-select the option {Ornaments & Tremolos}.