Nt32Pkg: Always use 0x2000 for maxim variable size

Currently the PcdMaxVariableSize is controlled by the below condition
check:

!if $(SECURE_BOOT_ENABLE) == TRUE || $(TLS_ENABLE) == TRUE
  gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
!endif

But for other case, PcdMaxVariableSize is also required with the value
of 0x2000 (e,g. NetworkPkg/IScsiDxe), so remove the condition of
PcdMaxVariableSize for NT32 platform.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jiaxin Wu <jiaxin.wu@intel.com>