Avoid double deleting the wc_products_onsale transient.
Revert "Avoid double deleting the wc_products_onsale transient."

This reverts commit 3d0c08453086411c3bf9e9438f4f10b54810c5a7.
Use delete_transient method instead of a custom query.
Merge pull request #3262 from kayue/bug/double-deleteing-in-clear-product-transients

Fix double deleteing in clear product transients.