$ sudo apt-get remove git-annex 

Uninstall git-annex including dependent package

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

$ sudo apt-get remove --auto-remove git-annex 

Use Purging git-annex

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

$ sudo apt-get purge git-annex 

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 git-annex 

See Also,