maint: Remove unneeded input validation from internal fcns in private/ directories. * scripts/general/private/__isequal__.m, scripts/general/private/__splinen__.m, scripts/image/private/__imwrite__.m, scripts/image/private/ind2x.m, scripts/miscellaneous/private/__xzip__.m, scripts/miscellaneous/private/display_info_file.m, scripts/pkg/private/describe.m, scripts/pkg/private/get_forge_pkg.m, scripts/pkg/private/unload_packages.m, scripts/plot/private/__actual_axis_position__.m, scripts/plot/private/__add_datasource__.m, scripts/plot/private/__clabel__.m, scripts/plot/private/__errcomm__.m, scripts/plot/private/__errplot__.m, scripts/plot/private/__fltk_print__.m, scripts/plot/private/__gnuplot_get_var__.m, scripts/plot/private/__go_draw_axes__.m, scripts/plot/private/__go_draw_figure__.m, scripts/plot/private/__interp_cube__.m, scripts/plot/private/__line__.m, scripts/plot/private/__next_line_color__.m, scripts/plot/private/__next_line_style__.m, scripts/plot/private/__plt__.m, scripts/plot/private/__pltopt__.m, scripts/signal/private/rectangle_lw.m, scripts/signal/private/rectangle_sw.m, scripts/signal/private/triangle_lw.m, scripts/signal/private/triangle_sw.m, scripts/sparse/private/__sprand_impl__.m, scripts/statistics/models/private/logistic_regression_derivatives.m, scripts/statistics/models/private/logistic_regression_likelihood.m: Remove unneeded input validation from internal fcns in private/ directories.

--- a/scripts/plot/private/__gnuplot_get_var__.m
+++ b/scripts/plot/private/__gnuplot_get_var__.m
@@ -26,10 +26,6 @@
 
 function gp_var_value = __gnuplot_get_var__ (h, gp_var_name, fmt = "")
 
-  if (nargin < 2)
-    print_usage ();
-  endif
-
   if (numel (h) == 1 && isfigure (h))
     if (isempty (get (gcf, "__plot_stream__")))
       ostream = __gnuplot_open_stream__ (2, h);
@@ -56,7 +52,7 @@
   if (use_mkfifo)
     gpin_name = tmpnam ();
 
-    ## Mode: 6*8*8 ==  0600
+    ## Mode: 0600 == 6*8*8
     [err, msg] = mkfifo (gpin_name, 6*8*8);
 
     if (err)