pngminus: Remove a workaround for an old printer

A downgrade from 16-bit samples to 8-bit samples, or an expansion from
1- or 2-channel grayscale (or grayscale+alpha) to 3- or 4-channel
RGB (or RGB+alpha), etc., may be deemed generally useful. Such image
transforms could be made available to the user via command-line options.
On the other hand, keeping the decision to disable or enable these
transforms unconditionally at compile time (e.g. because they're needed
to work around a specific printer's limitations) is less than ideal.

contrib/pngminus/CHANGES.txt

@@ -11,3 +11,4 @@ version 1.0 - 1999.10.15 - First version.
         1.6 - 2018.08.05 - Improve portability and fix style (Cosmin Truta)
         1.7 - 2019.01.22 - Change license to MIT (Willem van Schaik)
         1.8 - 2024.01.09 - Fix, improve, modernize (Cosmin Truta)
+        1.9 - 2025.01.10 - Delete conditionally-compiled code (Cosmin Truta)

contrib/pngminus/png2pnm.c

@@ -235,22 +235,6 @@ BOOL do_png2pnm (png_struct *png_ptr, png_info *info_ptr,
   /* set up (if applicable) the expansion of grayscale images to bit-depth 8 */
   png_set_expand_gray_1_2_4_to_8 (png_ptr);
 
-#ifdef NJET
-  /* downgrade 16-bit images to 8-bit */
-  if (bit_depth == 16)
-    png_set_strip_16 (png_ptr);
-  /* transform grayscale images into full-color */
-  if (color_type == PNG_COLOR_TYPE_GRAY ||
-      color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
-    png_set_gray_to_rgb (png_ptr);
-  /* if the PNG image has a gAMA chunk then gamma-correct the output image */
-  {
-    double file_gamma;
-    if (png_get_gAMA (png_ptr, info_ptr, &file_gamma))
-      png_set_gamma (png_ptr, (double) 2.2, file_gamma);
-  }
-#endif
-
   /* read the image file, with all of the above image transforms applied */
   png_read_png (png_ptr, info_ptr, 0, NULL);