Two things (but I think the resolution will be the same)
You didn't mention the WordPress version (but I don't think it matters). And - I am going to presume that LAMPP is running locally (on the machine you are at)
I do a good amount of WordPress work and customization. What you are experiencing is a by product of WordPress being designed for shared hosting. It is 'assuming' you are connected to a server where the WordPress user uploads files via FTP AND is on a remote machine. That's not the case when you are working on the 'console machine'. By way of explanation, on a shared server the FTP user is almost always the 'owner' of the files in the Document Root. Wordpress is using FTP effectively as a 'proxy' -- that's how the 'auto-upgrade' also works.
(Its the same with XAMPP for Windows, same issue)
There are two possible fixes:
One: Get ProFTPd working and configured exactly as your Wordpress is. I.E. exact URL (hostname or IP) as set in your wp-config.php. He defualt user/owner for all files in /opt/lampp/htdocs is a special Linux user 'nobody'.
Two: I'm pretty sure you can remove the plugins manually without any problems. AFAIK, WordPress plugins are self contained - and - WordPress discovers them by enumerating the /wp-content/plugins folder. (its just like themes in that sense). I think just removing the folder will do the trick.http://codex.wordpress.org/Managing_Plugins