To uninstall upstart-watchdog just follow these instructions.
/ubuntu/vivid/universe///install/index.html watchdog jobs to reboot when system or session jobs fail Ubuntu 15.04 universe/utils 0.3
sudo apt-get remove upstart-watchdog
Which will remove just the upstart-watchdog package itself.
sudo apt-get remove --auto-remove upstart-watchdog
This will remove the upstart-watchdog package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for upstart-watchdog then this will work.
sudo apt-get purge upstart-watchdog
Or similarly, like this upstart-watchdog
sudo apt-get purge --auto-remove upstart-watchdog
|Description||watchdog jobs to reboot when system or session jobs fail|