Vlv2TbltDevicePkg/Capsule: Do not clear UEFI varstore

Vlv2TbltDevicePkg/Capsule: Do not clear UEFI varstore

Preserve the UEFI Variable store when a capsule update is
performed.  UEFI Variables are used to store firmware version
information for the sample devices (Red, Green, Blue).

Cc: Zailiang Sun <zailiang.sun@intel.com>
Cc: Yi Qian <yi.qian@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Zailiang Sun <zailiang.sun@intel.com>
Reviewed-by: Yi Qian <yi.qian@intel.com>