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/statistics/models/private/logistic_regression_derivatives.m
+++ b/scripts/statistics/models/private/logistic_regression_derivatives.m
@@ -30,10 +30,6 @@
 
 function [dl, d2l] = logistic_regression_derivatives (x, z, z1, g, g1, p)
 
-  if (nargin != 6)
-    print_usage ();
-  endif
-
   ## first derivative
   v = g .* (1 - g) ./ p; v1 = g1 .* (1 - g1) ./ p;
   dlogp = [(diag (v) * z - diag (v1) * z1), (diag (v - v1) * x)];