Date: Optimize the usage of moment-timezone to save some kilobytes

[gziolo]

Description

With the latest update of moment-timezone library there is a huge increase of the timezones data to be bundled by default. This is the consequence of the bug fix added in moment/moment-timezone#697. It turns out that JSON data is now at 925kB in 0.5.23 version: https://unpkg.com/moment-timezone@0.5.23/data/packed/latest.json. This is a big change comparing to the version 0.5.16 which we still bundle in Gutenberg: https://unpkg.com/moment-timezone@0.5.16/data/packed/latest.json - 126kB.

This PR stops including JSON metadata for timezones because we use WordPress specific timezone in here:
https://github.com/WordPress/gutenberg/blob/master/packages/date/src/index.js#L94-L99
It turns out all that data is never consumed in the application and is useless. This opens some nice improvements for the size of the date bundle.

Before

./build/date/index.js 187 KiB 24 [emitted] date

After

./build/date/index.js 13.2 KiB 24 [emitted] date

How has this been tested?

npm test

Check whether scheduling posts still works as expected in Gutenberg.

Types of changes

Refactoring towards lower bundle size.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[gziolo]

Those dependencies are never used...

[gziolo]

@atimmer, given that WordPress Core bundles moment-timezone version 0.5.23, I'm wondering how much it will influence the bundle size there :)

[ntwb]

👍

[marharyta]

@gziolo this is great, when are you releasing?

[gziolo]

It will be included in the upcoming Gutenberg plugin update this or next week (depending on how testing goes). It should be also included in WordPress core in a week or so. Not sure what is the timeline for that, to be honest. This year is safer to say :)