e2fsck: Suppress "orphan file is clean" message in preen mode

e2fsck: Suppress "orphan file is clean" message in preen mode

The e2fsck report, "Feature orphan_present is set but orphan file is
clean" is intended to request permission before removing the r/o
compat feature, orphan_present.  However, it is normal if the orphan
file is empty, and removing the r/o compat feature is a good thing so
that the file system can be mounted on older kernels.

When a file system with an orphan_file feature is mounted, the
orphan_present feature is set, and it is cleared when the file system
is cleanly unmounted.  IF the sytstem crashes when there are no inodes
in the orphan file, e2fsck should just silently clear the flag in
preen mode.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>