Remove custom webpack configs since wp-polyfill is no longer included by default

[douglas-johnson]

According to this:
https://github.com/thoughtis/cata-blocks/blob/0.3.8/blocks/newsletter/webpack.config.js#L12

We were waiting for this to hit a tagged release of wp scripts because it remove wp-polyfill from front-end scripts without the need for a custom webpack config:
WordPress/gutenberg#35436

Acceptance Criteria

• Blocks still build
• wp-polyfill is not enqueued on the front-end as a requirment of our blocks.