KVM: TDX: Fold tdx_sept_zap_private_spte() into tdx_sept_remove_private_spte()

KVM: TDX: Fold tdx_sept_zap_private_spte() into tdx_sept_remove_private_spte()

Do TDH_MEM_RANGE_BLOCK directly in tdx_sept_remove_private_spte() instead
of using a one-off helper now that the nr_premapped tracking is gone.

Opportunistically drop the WARN on hugepages, which was dead code (see the
KVM_BUG_ON() in tdx_sept_remove_private_spte()).

No functional change intended.

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030200951.3402865-18-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>