remove surface=undefined ; not a valuable tag

Making this pull request on behalf of @AndrewBuck who was having problems with git.... 


surface=undefined is pretty superfluous tag and I'd agree. 
http://taginfo.openstreetmap.org/tags/surface=undefined
If the surface is not known, why would you need to include the tag at all.

@AndrewBuck could explain more if he'd like.