To remove a compliance objective and the controls it created for any information system, you essentially follow the same procedure you followed to add the objective and its associated controls: Go to information systems; edit the system; de-select the objective you no longer desire and then hit save when you get to the last screen.
As with the adding process, you will now need to approve the deletion of the controls, so go to the pending approval section and you will see a new group. The group can either be approved on an individual level or if you selected "none" prior to entering that grouping, you can bulk approve all the deletions.