SimicsOpenBoardPkg: Fix GCC build issues

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2162



Removed unused functions in SecMain.c and
BdsPlatform.c.

Cc: David Wei  <david.y.wei@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Ankit Sinha <ankit.sinha@intel.com>
Cc: Agyeman Prince <prince.agyeman@intel.com>
Cc: Kubacki Michael A <michael.a.kubacki@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>

Signed-off-by: Prince Agyeman <prince.agyeman@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>
Reviewed-by: Michael Kubacki <michael.a.kubacki@intel.com>