A few months ago I installed this ppa from the recommendation of this answer. It now turns out that it's buggy as hell and breaks nearly everything almost all the time.
I tried removing the ppa and reinstalling unity, but I get the message
Reinstallation of unity is not possible, it cannot be downloaded.
How do I go back to using unaltered Unity?
If you have already removed the ppa, you have to add it again for this to work:
sudo apt-add-repository ppa:mc3man/systray-white
sudo apt-get update
Next, purge the ppa, which will remove it from your sources and restore the packages to the official version:
sudo ppa-purge ppa:mc3man/systray-white
In case ppa-purge is not installed, do:
sudo apt-get install ppa-purge
