How do I remove an approval process from a ticket?

While you can't remove the approval process once the ticket is in flight, you can override the approval steps as a technician.  This would eliminate the need to await approval.

to remove it permanently, you'd need to modify the approval process itself

if you open up an approval process you can then go to the "Request Types supported" tab and remove the ones that you no longer wish to be associated:

Thank you. I found out I had to be an admin in order to override approval steps.

Make sure your Techs don't change the Request Type to one which does not have an Approval Process to try and stop it, this brings issues if it is half way through the Approval stage!