Changing the Variant Title to Default didn't work for me, but then I tried something else which worked!
In the variant section of the product page, there are checkboxes next to each variant and one at the top to select all. Select all variants and then go to the Actions Menu and click Delete Variants. This gets rid of all variants and reverts the product page back to how it looks with a product with no variants.
You can delete variants from a product.