If you want it to only apply to your Plurk layout and not everyone else's:
Change this: url-prefix("http://www.plurk.com/")
To this: url("http://www.plurk.com/YOUR-USERNAME-HERE")

Alternately, if using Stylish, just edit the URL in the "Applies to" field.

If you want to blank out the whole Friends section (friends, mutual friends, avatars):
Change this: div.show_all_friends
To this: div#dash-friends-pics