Remove temporary `new_topics` route when all services are using Simorgh powered topics pages

[jroebu14]

Is your feature request related to a problem? Please describe. When all services are using Simorgh topics pages, we need to remove the temporary topics (/new_topics/) route that was set up in this PR

Describe the solution you'd like A clear and concise description of what you want to happen.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Testing notes [Tester to complete]

Dev insight: Will Cypress tests be required or are unit tests sufficient? Will there be any potential regression? etc

• [ ] This feature is expected to need manual testing.

Checklist

• [ ] (BBC contributors only) This issue follows the repository use guidelines

Additional context Add any other context or screenshots about the feature request here.