$ sudo apt-get remove libpq5 

Uninstall libpq5 including dependent package

If you would like to remove libpq5 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove libpq5 

Use Purging libpq5

If you use with purge options to libpq5 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge libpq5 

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 libpq5 

See Also,