You can delete it from the standard list.  The transactions and descriptions would remain with the job according to this:  https://us-kb.sage.com/portal/app/portlets/results/viewsolution.jsp?solutionid=223924350033231&page=1&position=3&q=delete%20code%20code 

If you delete a cost code from the Standard Cost Code list, it won't affect the jobs. Once a cost code is associated with a  job, it lives in the job. For example, you can change the description of a cost code on a job without affecting the description in the standard cost code list.