There's a great tool to manipulate friends into list as raised here.
Though we cannot quickly/batch delete all friends in a list.
If you know how to do this, please share.
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A while ago, I had to delete friends in a list I had previously maintained. For that purpose, I used this userscript. http://userscripts.org/scripts/show/43404
The script works out of the box in Google Chrome and requires you to install Greasemonkey extension in Firefox. I reckon it should work fine in other web browsers as well.