KVM: x86/mmu: Remove unused field mmio_cached in struct kvm_mmu_page

After reverting and restoring the fast tlb invalidation patch series,
the mmio_cached is not removed. Hence a unused field is left in
kvm_mmu_page.

Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Jia He <justin.he@arm.com>
Message-Id: <20210830145336.27183-1-justin.he@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu_internal.h

@@ -37,7 +37,6 @@ struct kvm_mmu_page {
 
 	bool unsync;
 	u8 mmu_valid_gen;
-	bool mmio_cached;
 	bool lpage_disallowed; /* Can't be replaced by an equiv large page */
 
 	/*