Remove periodic grids

merged

mentioned in commit 2771194a

@oliver.sander I'm slightly surprised... wouldn't it have been desirable to get periodic meshes working again?

Well,

• Nobody has used this feature for the last 15 years
• I don't know how it is supposed to work. I wouldn't even know where to start to get it working again.
• There is no documentation for this at all.

@peter , do you know more about this?

No, I don't know anything about periodic grids in UG. Never used it, just remember some diploma thesis in Gabriel's group ages ago. I agree with Oliver that you don't want to do this.

OK. Thanks for clearification.