ClevoOpenBoardPkg/N1xxWU: Remove unused PCD 'PcdUseHpetTimer'

For N1xxWU, it is using the HPET timer unconditionally. The PCD
'PcdUseHpetTimer' is not being used.

This commit will remove the usage of the above PCD in package DSC files.

Cc: Ankit Sinha <ankit.sinha@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Michael Kubacki <michael.a.kubacki@intel.com>