I removed the files, video, photos and friends lenses with the following command.
sudo apt-get purge unity-lens-files unity-lens-video unity-lens-photos unity-lens-friends
Although the corresponding results have disappeared from dash, only the friends tab has been removed.
There still are tabs for files, video and photos, albeit empty.
How do I remove these empty tabs? I use Ubuntu 13.10 Saucy Salamander.
I understand that this issue didn't exist in 12.04. The directory structure of unity lenses seems to have changed from 12.04 to 13.10. Earlier the lenses were stored in
/usr/share/unity/lenses/. That isn't the case now, rendering this answer inappropriate: http://askubuntu.com/a/120116/111720