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/__errplot__.m
+++ b/scripts/plot/private/__errplot__.m
@@ -17,7 +17,7 @@
 ## <http://www.gnu.org/licenses/>.
 
 ## -*- texinfo -*-
-## @deftypefn {Function File} {@var{h} =} __errplot__ (@var{fstr}, @var{p}, @dots{})
+## @deftypefn {Function File} {@var{h} =} __errplot__ (@var{fstr}, @var{hax}, @dots{})
 ## Undocumented internal function.
 ## @end deftypefn
 
@@ -25,11 +25,7 @@
 ## Author: Teemu Ikonen <tpikonen@pcu.helsinki.fi>
 ## Keywords: errorbar, plotting
 
-function h = __errplot__ (fstr, p, varargin)
-
-  if (nargin < 4 || nargin > 8) # at least two data arguments needed
-    print_usage ();
-  endif
+function h = __errplot__ (fstr, hax, varargin)
 
   [fmt, valid] = __pltopt__ ("__errplot__", fstr);
 
@@ -55,7 +51,7 @@
       ifmt = "yerr";
     endif
 
-    hg = hggroup ("parent", p);
+    hg = hggroup ("parent", hax);
     h = [h; hg];
     args = __add_datasource__ ("__errplot__", hg,
                                {"x", "y", "l", "u", "xl", "xu"});