LU-4315 doc: correct lfs migrate man page separation

LU-4315 doc: correct lfs migrate man page separation

The "--block" and "--non-block" options are not relevant for
lfs-setstripe.1, only lfs-migrate.1 so move their descriptions
there.

Also remove duplicate setstripe option descriptions from
lfs-migrate.1, since they are becoming increasingly complex.
Instead, just refer to the lfs-setstripe.1 man page for other
options.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I13a28b33be2dc29aa0f44d177a62dbd2e13ebbe5
Reviewed-on: https://review.whamcloud.com/31406
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>