curveopt: try simple, but no good

curveopt: try simple, but no good

It seems to just shrink the simplex and then exit.  I think it doesn't
manage to find the narrow trench in configuration space in which
possible improvements lie.

Also tried gsl_multimin_fminimizer_nmsimplex but this is even slower
than siman.  So we will go back to siman now.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>