2.0/Space Age: Why is there a surface called "NiceFill_*****" in the remote view?
Please read the "How does NiceFill work?" section as well.
The remote view is a new feature available in Factorio 2.0/Space Age, and shows all surfaces, even the ones generated by NiceFill. It is unknown whether it's possible to hide these surfaces from the remote view. Fortunately, it's not possible to go to these surfaces unless you're using commands, so it's best to just ignore them. If surfaces can be hidden in the future, then the mod will be updated. Has been fixed in 1.1, and all existing NiceFill surfaces will be hidden.

2.0/Space Age: I cannot remove Landfill with the mod installed
Please read the "How does NiceFill work?" section as well.
Removing Landfill is a new feature in Factorio 2.0. NiceFill replaces the Landfill you've placed down with the actual tile it finds on the surface copy. Because of this the tile is no longer considered to be Landfill by the game, but actual grass, dirt, sand, etc., and these tiles cannot be removed.

How does NiceFill work?
When placing Landfill, instead of having to guess what the appropriate replacement tile would have to be like in earlier versions of the mod, NiceFill generates a copy of the surface, excluding all the tiles Landfill can be placed on.
For Nauvis, this means it generates a copy without any of the water tiles. To improve performance it also excludes all cliffs, decoratives and other entities.
Using the surface copy, NiceFill knowns exactly which tile it has to replace the Landfill with.