BUG: Build files with wp element not react (fixes #953)

[nerrad]

Problem this Pull Request solves

See #953 for background. Basically this pull removes a configuration from the babel configuration file so that built files for the EE assets use wp.element.createElement instead of React.createElement. Note, any dependencies that import react will still use react.createElement but that still utilizes the WP external via the dependency extractor plugin (which effectively means that the version of react used will always be whatever is bundled with WP).

How has this been tested

• Impacts Event Attendees block so ensure it still works as expected (breakage would result in it not loading/working at all, so easy to verify).
• Impacts exit modal on plugins page for EE deactivation because the exit modal package depends on React. Easy to verify, if it shows up then it's working.
• Make sure there are no console errors related to the above when testing (there are some in the block editor but are unrelated to these changes and pre-existing).

Checklist

• I have read the documentation relating to systems affected by this pull request, see https://github.com/eventespresso/event-espresso-core/tree/master/docs
• User input is adequately validated and sanitized
• all publicly displayed strings are internationalized (usually using esc_html__(), see https://codex.wordpress.org/I18n_for_WordPress_Developers)
• My code is tested.
• My code follows the Event Espresso code style.
• My code has proper inline documentation.
• My code accounts for when the site is in Maintenance Mode (MM2 especially disallows usage of models)

[tn3rb]

what about the comment right above this line?

this is needed because plugin exit modal uses react not wp.element

[nerrad]

oh ya, the comment could have been removed too! Dunno how I missed that.

[nerrad]

Fixed in ffb080c