Fix implementation of hook_ds_layout_info_alter()

Well, the easiest way is an alter hook before all layouts are returned (easy, takes 5 minutes) or even an interface to select layouts you only want to make available (easy too, but takes some time). So hook and/or UI, all good for me, will try to come up with a patch somewhere this week.

Alright, dev now has an alter hook, e.g.

/**
 * Implements hook_ds_layout_info_alter().
 */
function hook_ds_layout_info_alter(&$layouts) {
  unset($layouts['ds_2col']);
}

Hi, is this available in 8.x? It's implemented by ds_extras but not documented in ds.api.php.

Well, layouts are discovered through layout_plugin module, which should have an alter, so you can remove them there normally.

We use the layout plugin module now.

Looking at this code, the hook should be "hook_layout_alter(&$plugin_definitions)"
http://cgit.drupalcode.org/layout_plugin/tree/src/Plugin/Layout/LayoutPl...

The drush command is also broken, my colleague is working on that next week.

related: #2571341: hook_ds_layout_info does not exist anymore

Updating metadata, relating issue from #9.

Let's see what bot thinks...