SimicsOpenBoardPkg: Remove logic that loads variable from disk file

Simics QSP platform always supports flash devices.
The logic that was ported from OVMF where the flash devices might
not be supported in some configurations is useless in QSP platform.
So, the patch removes all of them.

Signed-off-by: Ray Ni <ray.ni@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Reviewed-by: Zhiguang Liu <zhiguang@liu@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>