NFS: Remove a bogus flag setting in pnfs_write_done_resend_to_mds

Since pnfs_write_done_resend_to_mds() does not actually call
end_page_writeback() on the pages that are being redirected to the
metadata server, callers of fsync() do not see the I/O as complete until
the writeback to the MDS finishes. We therefore do not need to set
NFS_CONTEXT_RESEND_WRITES, since there is nothing to redrive.

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