LU-3953 build: Fix duplicate snmp directory packaging

LU-3953 build: Fix duplicate snmp directory packaging

The %{_datadir}/lustre/snmp/mibs is in conflict with the later
%{_datadir}/lustre in the %files section.  Fortunately, it just
prints a warning rather than aborting the process.  But we can
fix that warning.

We remove the more specific %{_datadir}/lustre/snmp/mibs since
the files are already included with the more general form.

Change-Id: I293f0bf07760719f7cf3e1a963e49c007a483311
Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-on: http://review.whamcloud.com/18191
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>