KVM: x86: Remove spurious kvm_mmu_unload() from vcpu destruction path

x86 does not load its MMU until KVM_RUN, which cannot be invoked until
after vCPU creation succeeds.  Given that kvm_arch_vcpu_destroy() is
called if and only if vCPU creation fails, it is impossible for the MMU
to be loaded.

Note, the bogus kvm_mmu_unload() call was added during an unrelated
refactoring of vCPU allocation, i.e. was presumably added as an
opportunstic "fix" for a perceived leak.

Fixes: fb3f0f51

 ("KVM: Dynamically allocate vcpus")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>