$ sudo apt-get remove pg-activity 

Uninstall pg-activity including dependent package

If you would like to remove pg-activity and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove pg-activity 

Use Purging pg-activity

If you use with purge options to pg-activity package all the configuration and dependent packages will be removed.

$ sudo apt-get purge pg-activity 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove pg-activity 

See Also,