Remove Babel polyfill from Slideshow block

[simison]

Partly resolves #31689

Initially, I thought we could remove this dependency when we move blocks to Jetpack, but @jsnajdr is upgrading Babel setup in Calypso and this method of polyfilling is being deprecated.

Changes proposed in this Pull Request

Testing instructions

• Build blocks:

   npm ci
   npx lerna bootstrap --concurrency=2 --scope='@automattic/jetpack-blocks'
   npx lerna run build --stream --scope='@automattic/jetpack-blocks' -- -- --output-path /path/to/jetpack/_inc/blocks/ --watch
  

• Apply Add wp-polyfill as a dependency for Slideshow block jetpack#11657 in Jetpack
• Add Slideshow block in the editor (don't add any other blocks to mess up results)
• Open the page with the block
• Note from networks tab how wp-polyfill loads
• Block works in IE11

[matticbot]

Test live: https://calypso.live/?branch=update/slideshow-remove-babel-polyfill

[ockham]

Works fine with Automattic/jetpack#11657 👍

[jsnajdr]

👋 @simison and @ockham ! After the @babel/polyfill usage got removed here, it doesn't need to be as a dependency in package.json any more. Done in a follow-up PR #31711. Please 👀