fscrypt: remove unneeded empty fscrypt_operations structs

In the case where a filesystem has been configured without encryption
support, there is no longer any need to initialize ->s_cop at all, since
none of the methods are ever called.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Acked-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>