remove WhiteIsZero i8 test

tests/decode_images.rs

@@ -236,11 +236,6 @@ fn test_tiled_oversize_gray_i8() {
     test_image_sum_i8("tiled-oversize-gray-i8.tif", ColorType::Gray(8), 1214996);
 }
 
-#[test]
-fn test_tiled_whiteiszero_gray_i8() {
-    test_image_sum_i8("tiled-whiteiszero-gray-i8.tif", ColorType::Gray(8), 1214996);
-}
-
 #[test]
 fn test_tiled_cmyk_i8() {
     test_image_sum_i8("tiled-cmyk-i8.tif", ColorType::CMYK(8), 1759101);