$ sudo apt-get remove gally 

Uninstall gally including dependent package

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

$ sudo apt-get remove --auto-remove gally 

Use Purging gally

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

$ sudo apt-get purge gally 

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 gally 

See Also,