Ubuntu One is a cloud storage service operated by Canonical Ltd. Canonical announced that they are going to shut down the service. Ubuntu One service is integrated with Ubuntu Operating system. You can remove Ubuntu One packages by apply following commands in a terminal.
sudo apt-get autoremove ubuntuone-client python-ubuntuone-control-panel
Clean system cache
sudo apt-get autoremove
sudo apt-get autoclean
sudo apt-get autoclean