generic/398: remove workarounds for wrong error codes

generic/398: remove workarounds for wrong error codes

generic/398 contains workarounds to allow for renames of encrypted files
to fail with different error codes.  However, these error codes were
fixed up by kernel commits f5e55e777cc9 ("fscrypt: return -EXDEV for
incompatible rename or link into encrypted dir") and 0c1ad5242d4f
("ubifs: switch to fscrypt_prepare_rename()").

It's been long enough, so update the test to expect the correct behavior
only, so we don't accidentally reintroduce the wrong behavior.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>