KVM: MMU: remove unused struct kvm_unsync_walk

Remove 'struct kvm_unsync_walk' since it's not used.
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/mmu.c

@@ -173,11 +173,6 @@ struct kvm_shadow_walk_iterator {
 	     shadow_walk_okay(&(_walker));			\
 	     shadow_walk_next(&(_walker)))
 
-
-struct kvm_unsync_walk {
-	int (*entry) (struct kvm_mmu_page *sp, struct kvm_unsync_walk *walk);
-};
-
 typedef int (*mmu_parent_walk_fn) (struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp);
 
 static struct kmem_cache *pte_chain_cache;