Remove ig.Entity._wmInEditor property?

[Joncom]

https://github.com/phoboslab/Impact/blob/425cbc119d2ecde26b11d071ee6e79ec2fa92c27/lib/weltmeister/edit-entities.js#L343

As far as I can tell this doesn't get used anywhere...

Furthermore, there are other ways of detecting if the editor is running:

if( ig.global.wm ) { /* running weltmeister */ }
if( ig.editor ) { /* running weltmeister */ }

Is there really any need to add this information to every single entity?