$ sudo apt-get remove gst123 

Uninstall gst123 including dependent package

If you would like to remove gst123 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove gst123 

Use Purging gst123

If you use with purge options to gst123 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge gst123 

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 gst123 

See Also,