Checkpoint/Restart: Don't use shell prefix when describing batch scripts

There is a shell prefix on https://gitlab.hrz.tu-chemnitz.de/zih/hpcsupport/hpc-compendium/-/blob/preview/doc.zih.tu-dresden.de/docs/jobs_and_resources/checkpoint_restart.md#L67, however, the text before this snippet mentions batch scripts. Should the text be changed? Should one provide more batch script context?

The change was introduced by !532 (merged).