flexfiles: remove pointless setting of NFS_LAYOUT_RETURN_REQUESTED

Setting just the NFS_LAYOUT_RETURN_REQUESTED flag doesn't do anything,
unless there are lsegs that are also being marked for return. At the
point where that happens this flag is also set, so these set_bit calls
don't do anything useful.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>