Remove unused exit code constants
Remove unused exit code constants

There is a duplicate one under st2common/st2common/constants/exit_codes.py.

Plexxi/st2,StackStorm/st2,StackStorm/st2,nzlosh/st2,nzlosh/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2,nzlosh/st2,Plexxi/st2,Plexxi/st2,StackStorm/st2