Duplicated BuildHistory

Found in a `$JENKINS_HOME/config.xml`:

```
  <nodeProperties>
    <com.cloudbees.jenkins.plugins.mtslavescloud.BillingMemoBuilder_-BuildHistory plugin="mansion-cloud@1.22">
      <builds>
        …
      </builds>
    </com.cloudbees.jenkins.plugins.mtslavescloud.BillingMemoBuilder_-BuildHistory>
    <com.cloudbees.jenkins.plugins.mtslavescloud.BillingMemoBuilder_-BuildHistory reference="../com.cloudbees.jenkins.plugins.mtslavescloud.BillingMemoBuilder_-BuildHistory"/>
  </nodeProperties>
```