`btrfs check`: don't recommend to run --repair in some cases

[kdave]

Original report https://bugzilla.suse.com/show_bug.cgi?id=1094930 .

There's one stray recommendation to run check with --repair altough we discourage that everywhere. There's still one at check/main.c:10501. Analyze what can be done and give a safe recommendation or drop the line.