Revert "KVM: X86: Update mmu->pdptrs only when it is changed"

This reverts commit 24cd19a2.
Sean Christopherson reports:

"Commit 24cd19a2

 ('KVM: X86: Update mmu->pdptrs only when it is
changed') breaks nested VMs with EPT in L0 and PAE shadow paging in L2.
Reproducing is trivial, just disable EPT in L1 and run a VM.  I haven't
investigating how it breaks things."

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>