title: Removing records on module upgrade on OpenERP / ODOO
body: <p>I have an application module that have loaded employees for database initialization with 
  custom data in a previous module release:</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;openerp&gt;
      &lt;data&gt;
          ....
          &lt;!-- John Smith --&gt;
          &lt;record id="emp_john_smith" model="hr.employee"&gt;
              &lt;field name="name"&gt;John Smith&lt;/field&gt;
              &lt;field name="company_id" ref="base.main_company"/&gt;
              &lt;field name="department_id" ref="dp_production"/&gt;
              &lt;field name="job_id" ref="jb_production_officer"/&gt;
              &lt;field name="work_email"&gt;john@company.com&lt;/field&gt;
              &lt;field name="begin_date"&gt;2012-01-01&lt;/field&gt;
              &lt;field name="gender"&gt;male&lt;/field&gt;
              &lt;field name="work_location"&gt;Madrid&lt;/field&gt;
              &lt;field name="lang"&gt;es_ES&lt;/field&gt;            
          &lt;/record&gt;
      ....
      &lt;record id="ctr_john_smith_hr" model="hr.contract"&gt;
          &lt;field name="name"&gt;John Smith Production Contract&lt;/field&gt;
          &lt;field name="employee_id" ref="emp_john_smith"/&gt;
          &lt;field name="job_id" ref="jb_production_officer"/&gt;
          &lt;field name="email"&gt;john@company.com&lt;/field&gt;
          &lt;field name="date_start"&gt;2012-01-01&lt;/field&gt;
          &lt;field name="wage"&gt;0&lt;/field&gt;
          &lt;field name="percent_working_hours"&gt;15&lt;/field&gt;
          &lt;field name="working_hours" ref="spain_calendar"/&gt;
      &lt;/record&gt;
      &lt;/data&gt;
  &lt;/openerp&gt;
  </code></pre>
  
  <p>But these records must be removed on the next release of that module. Which is the record element i should use on the XML data file of the next release to erase those records?</p>