Remove 'type' from layouts.yml

So class can be seen in the layout annotation (Drupal\Core\Layout\Annotation\Layout.php).

But .. funny enough .. type is probably a leftover which simply doesn't exist anymore .. so we can probably just remove it :)
(probably from either in experimental phase, or maybe from panels, not sure)

That property was from the layout_plugin, but is not anymore in layout_discovery, so we can simply remove it.

commited and pushed