You sure can! While this is not currently possible on ifttt.com, you can permanently delete Applets on platform.ifttt.com.
If you’ve never visited the IFTTT platform before, you’ll need to sign up. But don't worry, this process only takes about 30 seconds and is completely free:
Click Start building, then enter your Company name. If you don't have a company, feel free to enter your name, username, or anything else you can think of.
Click Get started a couple of times, and you should be all set!
Now you can head back to platform.ifttt.com, click on the Applet you'd like to delete, and click Delete to permanently remove the Applet from your IFTTT account.
Note that if you'd like to delete an archived Applet, you'll need to temporarily Restore the Applet before being able to delete it.