Fixed captions on whatsapp audio

[SecondeJK]

This PR removes the ability to add a caption to a WhatsAppAudio Object.

Description

Captions are not supported on the API, so this shouldn't have been an available feature. Nothing will get rendered if you pass a caption in, though it will now throw a warning.

How Has This Been Tested?

Tests have been adjusted accordingly.

Example Output or Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• 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 read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.