`remove_dir_recurse()` in `dir.c` doesn't check for mount points, even
though this check was already added for `git clean` in #2268. So `git
worktree remove` (or anything else that calls it) will traverse NTFS
junctions and delete whatever is there. Similar to #607.
This extends the same check from #2268 but for anything that calls
`remove_dir_recurse()`.