Use fscrypt_policy_v2 from <linux/fscrypt.h>

Now that bionic's copy of linux/fscrypt.h has been updated to Linux 6.7,
it's no longer necessary for libfscrypt to have its own definition of
struct fscrypt_policy_v2.  This addresses a TODO in the code.

Bug: 299136786
Test: atest libfscrypt_unit_test
Change-Id: Ie8d5860774576ebdad956d72e0db88ae4186d5eb
1 file changed