Drop MS_DNS* options from ipup-post

[deekej]

... if possible. These are related to PPP, and there's probably not much people using it these days anyway. Also, NetworkManager does not support these values neither.

• [ ] Check what is actually using MS_DNS1 and MS_DNS2 these days.
• [ ] Check if we can safely drop it.
• [ ] Drop it from ipup-post.