Simplify the reference-results-metadata file

[MakisH]

The current metadata file is named reference-results-metadata.txt, but it is a Markdown file.

Some information in that file is not particularly useful: once the host is known, the CPU information is automatically known, and reproducibility across systems is not intended.

There is currently a missing blank line:

| PRECICE_UID | 1003 |
| PRECICE_GID | 1003 |
## Information about the machine

### uname -a

This PR:

• Renames the file from .txt to .md
• Removes the lscpu output (first added in Add Workflows for generating reference results  #410 (comment))
• Renames the function get_machine_informations() to get_machine_information()
• Simplifies the content of the metadata file to make the file shorter and easier to read.

Follow-up of #882.

Tested in https://github.com/precice/tutorials/actions/runs/31333057244, leads to:

<!---
This file has been generated by the generate_reference_results.py script and should not be manually modified
-->

# Reference results

- Archive: `fluid-openfoam_solid-cpp.tar.gz`
- Generated at: `2026-08-09 22:03:44`
- Host: `Linux precice-tests 5.15.0-186-generic #196-Ubuntu SMP Sat Jun 20 16:09:34 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux
`

## System tests arguments used to generate the results

| name | value |
| --- | --- |
| `PLATFORM` | `ubuntu_2404` |
| `CALCULIX_VERSION` | `2.20` |
...

[MakisH]

Actually, naming that .reference-results-metadata.md would place it at the top of the file list, at least for my archive manager. I can rename it tomorrow.

[PranjalManhgaye]

@MakisH looks good to me, and renaming to .md and dropping lscpu makes the metadata much easier to read, Thanks its much cleaner now