remove wrapper markup & classes from default region.html.twig

Problem/Motivation

Region.html.twig is adding yet another layer of templates, div & classes to Drupal, thats only usable in very specific cases.

Proposed resolution

Remove the default wrapper div & classes from region.html.twig, so its still usable for a theme that need that kind of flexibility.

region.html.twig

{% if content %}
    {{ content }}
{% endif %}

Remaining tasks

test bartik
test seven
write test
wrap markup classes out into the template

User interface changes

API changes