Currently the best and easiest way to bulk add or remove your variants would be via our CSV file. We do have the option to bulk delete products in your bulk editor but this is only at the product level and not done by variants.
If you have not already, you can take a look at our CSV guide along with our CSV template here: https://docs.shopify.com/manual/products/import-export
If you are looking to bulk edit your variants we do have a great app which can allow you to do this called Bulk Edit - https://apps.shopify.com/bulk-edit
I hope that helps and best of luck to you!