Review all bash scripts, and their input variables

See example: https://github.com/MetOffice/CMEW/pull/145#discussion_r1461767537

For any bash scripts we decide to keep, we should document at the top of the bash script which environmental variables are expected to be set for the bash script to run successfully (following a discussion between @ehogan and @chrisbillowsMO).

Depends on #136.

~Depending on the number of shell scripts remaining after this review, consider the use of `shellcheck` in the GitHub workflow and working practices.~ Now in #255.

Readability and understandability are the key to good maintenance; more than four commands should remain in a well-named bash script.

**Details**

- Estimate: Small-medium, suitable solo mission.
- Reviewer(s): Alistair

Time box:
- 0.5 day

Outcome
- Identify how many commands are run in each bash script and which variables. This will help us decide to remove the bash script or not. - Documentation at the top of the shell scripts that are kept.

Start by reviewing the repository's remaining bash scripts after checking the dependency on #136. For each script, identify its command count and input environment variables, then decide whether it should remain. Done means retained scripts document their expected environment variables at the top and the review records which scripts should be removed or kept.

Written by the indexing model from the issue text.