Remove unused Mozilla Monitor page banner

[alexgibson]

Description

There's an unused homepage banner for Mozilla Monitor that was never enabled and can likely be removed:

• https://github.com/mozilla/bedrock/blob/main/bedrock/base/templates/includes/banners/monitor-plus.html
• https://github.com/mozilla/bedrock/blob/main/bedrock/mozorg/templates/mozorg/home/includes/monitor-mid-banner.html
• https://github.com/mozilla/bedrock/blob/main/media/static-bundles.json#L204-L209
• https://github.com/mozilla/bedrock/blob/main/media/static-bundles.json#L1780-L1785

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Success Criteria

• [ ] Orphaned code is removed from the repo

[janbrasna]

This was disabled / replaced with fundraiser promo in #14552@9cef967 (5/24)