Don't duplicate enum params

The new docs look like:

```
  OPTIONS
         --stack-status-filter (list)
            Stack status to use as a filter. Specify one or  more  stack  status
            codes  to  list  only  stacks with the specified status codes. For a
            complete list of stack status codes, see the  StackStatus  parameter
            of the  Stack data type.

         Syntax:

            "string" "string" ...

            Where valid values are:
              CREATE_IN_PROGRESS
              CREATE_FAILED
              CREATE_COMPLETE
              ROLLBACK_IN_PROGRESS
              ROLLBACK_FAILED
              ROLLBACK_COMPLETE
              DELETE_IN_PROGRESS
              DELETE_FAILED
              DELETE_COMPLETE
              UPDATE_IN_PROGRESS
              UPDATE_COMPLETE_CLEANUP_IN_PROGRESS
              UPDATE_COMPLETE
              UPDATE_ROLLBACK_IN_PROGRESS
              UPDATE_ROLLBACK_FAILED
              UPDATE_ROLLBACK_COMPLETE_CLEANUP_IN_PROGRESS
              UPDATE_ROLLBACK_COMPLETE

```

Fixes #609.