Dave's answer is the correct one, here. It's much faster to delete interactive elements after the fact in Acrobat, because you can multi-select buttons. I don't know what it is about InDesign's incomplete & wonky forms implementation, but you can't select two buttons at once. The only way to affect multiple buttons at once is via scripting, where you'd collect all the buttons and then loop over them, actually the script would still be deleting them one at a time.
Worth pointing out here that if you are exporting to PDF from InDesign, then buttons won't export if you choose Print PDF from the file type dropdown when exporting. You'd need to select a specific option ("Appearance Only" in the "Interactive Elements" dropdown of the General section of the Export Adobe PDF dialog) to even see the non-working buttons onscreen in Acrobat.
If it's just one INDD document that you want to repurpose for print, Dave's way is the fastest.
If it's something you'd have to do repeatedly, I'm sure I could figure out how to adapt one of my form field scripts to mass delete buttons.