Make delete_attachment action hook helpful

[filosofo]

Similar to the situation with delete_user, the delete_attachment action hook fires off too late to be of much use: at that point the attachment and all of its data have been deleted.

People have complained about this  here and  here.

I grepped through the plugin repository, and of about 6200 plugins, only 5 use the delete_attachment hook: audit-trail, karailievs-sitemap, lumberjack, power-thumbnail, vivtiger-image-resizer. (One other one---scissors---complains in a comment about the fact that the hook can't be used at that point).

Of those plugins that use delete_attachment, it appears that none would be adversely affected by my patch. In fact, at least one (vivtiger-image-resizer) has a conditional block based on getting back post information from the id passed to the callback, something that currently cannot happen, so my patch should apparently keep it from having orphaned thumbnails.

(In [10400]) Move delete_attachment action up. Props filosofo. fixes #8909