KVM: VMX: Remove vcpu_vmx's defunct copy of host_pkru

KVM: VMX: Remove vcpu_vmx's defunct copy of host_pkru

Remove vcpu_vmx.host_pkru, which got left behind when PKRU support was
moved to common x86 code.

No functional change intended.

Fixes: 58a270f1d7721 ("KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200617034123.25647-1-sean.j.christopherson@intel.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>