[Newsletter Subscription Form Block] Sign up button disappear after submit

[thomasguillot]

If the form returns an error, the submit button disappear and it's not possible to re-submit the form.

Removing submit.remove( spinner ); (https://github.com/Automattic/newspack-newsletters/blob/trunk/src/blocks/subscribe/view.js#L81) stops the issue but there must be a better solution