Clean up remnants in mdrun

Clean up remnants in mdrun

nstlist < 0 is now impossible after the removal of group-scheme
heuristic neighbour-list updates, so remove some output that can no
longer be triggered.

Iterated constraints are no longer implemented, but some things got
left behind in the removal. Removed ekind_save variable from do_md,
and some comments. Removed some brace pairs that made reviewing the
removal of iterative integrators easy, because uncrustify would not
re-indent that patch. It now does that re-indent, but there's no
potential for bugs here.

deviceOptions was used for OpenMM support, but is now unused, so
removed.

GMX_WRITELASTSTEP has never had a way to be defined, so removed the
check for that.

Change-Id: If547b86a5ec05dce3bb591b8d4c6dd052c07c04e