CSV Import (refer to Suite Answers ID 26742) can be used to remove or set the Prices to Null of Items using Quantity Pricing. However, this could be a very tedious process for you need to separately map fields for each Price Level and corresponding Quantity Range.
We could mass remove the Quantity Pricing by:
1. Overwrite all items with a new Quantity Pricing Schedule.
2. Set the Quantity Pricing Schedule to Null (This can be done via CSV or Mass Update)
Please take note that the Quantity Pricing Schedule you would be using is not exclusive for a specific Unit of Measure (UOM)