Remove template files

### Description / Background

We'd like to remove the files at `scripts/templates`.

### Dependencies

Depends on:
- https://github.com/gchq/sleeper/issues/7273
- https://github.com/gchq/sleeper/issues/6284
- https://github.com/gchq/sleeper/issues/2384

Review dependency issues 7273, 6284, and 2384 first to confirm their work is complete. Then inspect the files under scripts/templates and remove them once no longer needed. Search for remaining references and run the relevant project checks; done means the templates are gone and no supported workflow depends on them.

Written by the indexing model from the issue text.