$ sudo apt-get remove gazebo7 

Uninstall gazebo7 including dependent package

If you would like to remove gazebo7 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove gazebo7 

Use Purging gazebo7

If you use with purge options to gazebo7 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge gazebo7 

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 gazebo7 

See Also,