KVM: x86/mmu: remove unused variable

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2119111



commit 31f6e383
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Mon Aug 1 07:27:18 2022 -0400

    KVM: x86/mmu: remove unused variable

    The last use of 'pfn' went away with the same-named argument to
    host_pfn_mapping_level; now that the hugepage level is obtained
    exclusively from the host page tables, kvm_mmu_zap_collapsible_spte
    does not need to know host pfns at all.

    Fixes: a8ac499b ("KVM: x86/mmu: Don't require refcounted "struct page" to create huge SPTEs")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>