Removed buggy -seppot output

ns() no longer computes forces, so the comment needs correcting.

dvdlambda was changed to an array at some point, but the output code
did not change in sync. So, that output has been broken in at least
4.6, and is always zero anyway. So the output code can go away.

A patch in master branch removes the useless parameters in the
neighbour-search code. When merging this patch into master branch,
eliminate the useless dvdlambda variable.

Fixes #1294

Change-Id: Iba48f549ee07f0ee1877035a9e506780439c8002