why-error.md: Cleanup and documenting (#9512)

Author: oech3

util/why-error.md

@@ -22,23 +22,19 @@ This file documents why some tests are failing:
 * gnu/tests/ptx/ptx-overrun.sh
 * gnu/tests/ptx/ptx.pl
 * gnu/tests/rm/one-file-system.sh - https://github.com/uutils/coreutils/issues/7011
-* gnu/tests/rm/rm1.sh
-* gnu/tests/rm/rm2.sh
+* gnu/tests/rm/rm1.sh - https://github.com/uutils/coreutils/issues/9479
 * gnu/tests/shred/shred-passes.sh
 * gnu/tests/sort/sort-continue.sh
 * gnu/tests/sort/sort-debug-keys.sh
 * gnu/tests/sort/sort-debug-warn.sh
-* gnu/tests/sort/sort-files0-from.pl
 * gnu/tests/sort/sort-float.sh
 * gnu/tests/sort/sort-h-thousands-sep.sh
 * gnu/tests/sort/sort-merge-fdlimit.sh
 * gnu/tests/sort/sort-month.sh
 * gnu/tests/sort/sort.pl
-* gnu/tests/stat/stat-nanoseconds.sh
 * gnu/tests/tac/tac-2-nonseekable.sh
 * gnu/tests/tail/end-of-device.sh
 * gnu/tests/tail/follow-stdin.sh
 * gnu/tests/tail/inotify-rotate-resources.sh
 * gnu/tests/tail/symlink.sh
-* gnu/tests/touch/obsolescent.sh
 * gnu/tests/tty/tty-eof.pl