Hide the second plan-term selector on mobile

[oswian]

Resolves #90362

Proposed Changes

Fixes the overlapping plan-term selectors on mobile by hiding the second instance. The second selector is redundant anyway, as there's another selector pinned to the top of the viewport.

Testing Instructions

1. Load /start/plans
2. Enable mobile viewport
3. Scroll down to the comparison grid
4. Check that the second plan-term selector is not displayed
5. Enable desktop viewport
6. Check that the second plan-term selector is displayed

Desktop (displayed)	Mobile (not displayed)

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-107876

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https://calypso.live?image=registry.a8c.com/calypso/app:build-107876&env=jetpack

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https://calypso.live?image=registry.a8c.com/calypso/app:build-107876&env=a8c-for-agencies

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[oswian]

The failing E2E tests don't appear to be related to this change.

[southp]

Works as described and LGTM 🚢

[oswian]

Thanks for the review @southp.

I just rebased and it has fixed the failing E2E tests ✅