[charcoal/attachment] Improve logic for deleting Attachments and descendants

[mcaskill]

The CollectionLoader should be used instead of the model factory to benefit from the dynamic type field feature to load the Attachment ID's sub-model.

charcoal/packages/attachment/src/Charcoal/Admin/Action/RemoveJoinAction.php

Lines 81 to 86 in c72eca8

	$attachment = $this->modelFactory()->create(Attachment::class)->load($attachmentId);
	$attachment = $this->modelFactory()->create($attachment['type'])->setData($attachment->data());
	if ($attachment['id'] !== null) {
	$attachment->delete();
	}