remove unused variable "ha"

this variable was causing a warning while compiling with gcc.

stb_image.h

@@ -2421,7 +2421,6 @@ static int stbi__parse_entropy_coded_data(stbi__jpeg *z)
                      for (x=0; x < z->img_comp[n].h; ++x) {
                         int x2 = (i*z->img_comp[n].h + x);
                         int y2 = (j*z->img_comp[n].v + y);
-                        int ha = z->img_comp[n].ha;
                         short *data = z->img_comp[n].coeff + 64 * (x2 + y2 * z->img_comp[n].coeff_w);
                         if (!stbi__jpeg_decode_block_prog_dc(z, data, &z->huff_dc[z->img_comp[n].hd], n))
                            return 0;