Remove benchmark example from docs

[rsanchez15]

Description

As the benchmark example was not refactored with Fast DDS v3, we are removing it from the documentation until we add it.

@Mergifyio backport 3.1.x 3.0.x

Fixes #5398

Contributor Checklist

• Commit messages follow the project guidelines.
• N/A Code snippets related to the added documentation have been provided.
• Documentation tests pass locally.
• Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• CI passes without warnings or errors.