Upsell Nudge: reduce excessive loading placeholders #13127002

Fixes Automattic/martech#2907

Proposed Changes

• This PR removes the excessive loading placeholders from the post-checkout Creator plan upsell. Now, the placeholder will only show where the price text is.

Note: This component also needs a cleanup since the quick start product is no longer in use.

Production:

This PR:

Testing Instructions

• Go to /checkout/<site slug>/offer-plan-upgrade/business/12345 for a site on the Explorer plan.
• Confirm that the loading placeholders are not shown and are only shown for the price.

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)?