While there isn't a complete way to remove the terms on invoices, you have the option to customise on what you want to show on your sales forms for your customers. Let's check your Custom form styles to edit the display settings. Here's how:
Click on the Settings icon.
Click on Custom form styles.
Click on Edit under Standard template.
Click on Content tab, and go to Display section.
Untick either one of Terms and Due date or expiration date.
Click on Done.
Check the preview page on the right to see the display on the sample invoice. You can always go back to the custom form styles section to edit your sales form.