Update namespace practices

[darylldoyle]

Description of the Change

As per #315, the WordPress minimum PHP version now supports namespaces and as such we shouldn't promote the use of pseudo namespaces anymore. This PR removes the mention of them from the best practices.

Verification Process

Tested locally.

Checklist:

• [x] I have read the CONTRIBUTING document.
• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [ ] All new and existing tests passed.

Applicable Issues

315

Changelog Entry

• Removed mention of pseudo namespaces as they're no longer required