fs: nfs: Fix statfs for NFS

Summary:
- I noticed that the results of the df command are incorrect for NFS.
- Finally, I found that obj_attributes is not needed to
  communicate with the NFS server on Linux
- This commit fixes this issue

Impact:
- None

Testing:
- Tested with spresense:rndis_smp

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

fs/nfs/nfs_proto.h

@@ -308,7 +308,6 @@ struct nfsv3_sattr
 struct nfs_statfs
 {
   uint32_t           obj_attributes_follow;
-  struct nfs_fattr   obj_attributes;
   nfsuint64          sf_tbytes;
   nfsuint64          sf_fbytes;
   nfsuint64          sf_abytes;