I remember going thru this a couple years ago.
WGT makes it a nice and painful process to delete friends. Can't select multiple people, can't delete all. You have to go to each individual profile and delete from there.
If you have hundreds of people that you want to delete, you're probably better off just creating a new profile and abandoning your current one, unless clicking a few hundred times to delete your friends is something you want to do.
Yes, I realize that people aren't supposed to have multiple accounts. But quite frankly, if my friends list starts to affect my swing meter again, I will not be going though the process of clicking 300 times to delete everyone off of my friends list again.