MC-1689: Remove unused experiment code

[mmiermans]

References

JIRA: MC-1689
Slack thread confirming this code can be removed

Description

Removes code for curated recommendation experiments that have finished, and will not be rolled out:

• 'The Big Rectangle' (TBR) including 'In the News' and Fakespot products.
• Extended expiration, where scheduled items from the last 4 days were shown.

PR Review Checklist

Put an x in the boxes that apply

• This PR conforms to the Contribution Guidelines
• The PR title starts with the JIRA issue reference, format example [DISCO-####], and has the same title (if applicable)
• [load test: (abort|skip|warn)] keywords are applied to the last commit message (if applicable)
• Documentation has been updated (if applicable)
• Functional and performance test coverage has been expanded and maintained (if applicable)

[jpetto]

i feel lighter just looking at this. nice! ty!