LU-4923 osd-ldiskfs: dirdata is not needed on MGS

LU-4923 osd-ldiskfs: dirdata is not needed on MGS

Don't print a warning message if the "dirdata" feature is not enabled
on MGS devices.  It is only needed for ldiskfs MDT devices.

Lustre-commit: 383ef1a93b67778704c009aa3c1b0e2c15a5bb76
Lustre-change: https://review.whamcloud.com/29274

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I1d8ccfc9c60eff128b480ea8efa298c1212c041a
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: https://review.whamcloud.com/32961
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>