Blender Git Loki

Outliner: modernize Purge operator.

That guy was still from the era where only way to remove an ID was to
save & reload the .blend file. Use modern code instead, should also be
much, much more efficient in big production files.

And that?s another nice occasion to add/test new batch ID deletion code, too. ;)

Related to T61276 Make Single User unlinks original object.