ubifs: remove unnecessary calls to set up directory key

In ubifs_unlink() and ubifs_rmdir(), remove the call to
fscrypt_get_encryption_info() that precedes fscrypt_setup_filename().
This call was unnecessary, because fscrypt_setup_filename() already
tries to set up the directory's encryption key.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>