libfscrypt: remove some hardcoded definitions

FS_ENCRYPTION_MODE_ADIANTUM and FS_POLICY_FLAG_DIRECT_KEY are in
Bionic's <linux/fs.h> now, so there's no need to define them in
libfscrypt anymore.

Test: compiled
Change-Id: I499a70a9f8fd3445098a1dd799b1aefe0fa374ce
1 file changed