CometlakeOpenBoardPkg: Remove unnecessary gPchSpiPpiGuid reference

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3307



The GUID is included in PeiPolicyUpdateLib.inf but not actually used.

Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Rangasai V Chaganty <rangasai.v.chaganty@intel.com>
Cc: Deepika Kethi Reddy <deepika.kethi.reddy@intel.com>
Cc: Kathappan Esakkithevar <kathappan.esakkithevar@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>