KVM: nVMX: delete meaningless nested_vmx_run() declaration

The function nested_vmx_run() declaration is below its implementation. So
this is meaningless and should be removed.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>