Adjust the function 'syn_spec_script_builder' to changes in the ATLAS12

code and SURFACE model atoms.

1) Account for the fact that all ATLAS12 computations now produce
   spectral energy distributions (SEDs) on a well-sampled uniform
   wavelength grid. Consequently, ATLAS12 computations with NLTE
   feedback from DETAIL no longer require a special treatment.
2) The function 'syn_spec_clean_grid' has become obsolete over the
   past years and has thus been removed.
3) The template 'make_fit_grid' has been revised to account for the
   changes related to the wavelength sampling in ATLAS12 and SURFACE.
   The fitting of spectra and SEDs should be faster now because the
   stored fluxes contain less data points and are pinned to a more
   uniform wavelength grid.