docs: update geometric median README (fixes #5899)

[unas0706]

This PR updates the README for the geometric median distribution:

• Updated return value in the example (1 → 0) to match L69.

• Removed an unused header file to clean up documentation.

• Read, understood, and followed the contributing guidelines

Resolves #5899

[stdlib-bot]

Hello! Thank you for your contribution to stdlib.

We noticed that the contributing guidelines acknowledgment is missing from your pull request. Here's what you need to do:

1. Please read our contributing guidelines.

2. Update your pull request description to include this checked box:

   - [x] Read, understood, and followed the [contributing guidelines](https://github.com/stdlib-js/stdlib/blob/develop/CONTRIBUTING.md)

This acknowledgment confirms that you've read the guidelines, which include:

• The developer's certificate of origin
• Your agreement to license your contributions under the project's terms

We can't review or accept contributions without this acknowledgment.

Thank you for your understanding and cooperation. We look forward to reviewing your contribution!

[stdlib-bot]

👋 Hi there! 👋

And thank you for opening your first pull request! We will review it shortly. 🏃 💨

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/geometric/median	$\color{green}167/167$ $\color{green}+100.00\%$	$\color{green}9/9$ $\color{green}+100.00\%$	$\color{green}2/2$ $\color{green}+100.00\%$	$\color{green}167/167$ $\color{green}+100.00\%$

The above coverage report was generated for the changes in this PR.

[kgryte]

Ref: #5990

[stdlib-bot]

Thank you for working on this pull request. However, we cannot accept your contribution as the issue this pull request seeks to resolve has already been addressed in a different pull request or commit.

Thank you again for your interest in stdlib, and we look forward to reviewing your future contributions.