Remove old/unused switches from www-config

[alexgibson]

Description

This is overdue, but it would be nice to do some spring cleaning of old/unused switches in the www-config repo:

https://github.com/mozmeao/www-config/blob/main/waffle_configs/bedrock-prod.env

We'd need to double check what's still in use in bedrock first.

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Success Criteria

• Unused switches are removed from the www-config repo

[janbrasna]

Most of older unused promo and experiment waffles removed:

• Remove old unused switches mozmeao/www-config#559

The rest was cleaned up:

• Clean up unused/removed switches mozmeao/www-config#582

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TODO/OQ:

• monitor-plus-banner got removed in Homepage and global nav updates #14552 but its assets are still kept, might need pruning as well if it's not coming back.
• challenge-the-default-active was originally used for product page takeover; now when it's a separate landing page its utility is somewhat questionable, I'm contemplating unconditionally showing the page without any switches in Fixup CTD landing & update promo link #14965 (comment) …

[janbrasna]

This was trimmed down in preparation for migrating to #15157 — there are only some possible followups mentioned above.