NFS: Remove a line of code that has no effect in nfs_update_inode()

Commit 0b467264 ("NFS: Fix attribute revalidation") changed the way
we populate the 'invalid' attribute, and made the line that strips away
the NFS_INO_INVALID_ATTR bits redundant.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>