Generally, it would be helpful to have the ability to undo edit actions throughout the system so that you can revert if you make an editing mistake.

In the short term, when deleting build steps, variables, etc. it would be helpful if the Audit log included the last known value for the item. For example, if you modify a step the Audit log includes View Settings and Diff Prev links, but if you delete a step the Audit log only includes a Step Was Deleted comment. If you inadvertently delete an item you have no way to know what the prior value was if you wish to restore it.