[FIX] crm: remove the field date_closed from demo data

Purpose:
The purpose of this commit is to change the current behavior of days to close
graph generating from customizable desk demo data.

Specification:
For the opportunities, the day_close field is a compute field depending upon the
date_closed field. For the customizable desk demo data, the date_closed field
pre-existed, due to that customizable desk opportunity was not won or lost but
the graph report was generated.
so, this commit fixes the current behavior for customizable desk opportunity.

Task-3278039

closes odoo/odoo#119292

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/crm/data/crm_lead_demo.xml

@@ -607,7 +607,6 @@ Andrew</p>]]></field>
             <field name="team_id" ref="sales_team.team_sales_department"/>
             <field name="user_id" ref="base.user_demo"/>
             <field name="stage_id" ref="crm.stage_lead3"/>
-            <field name="date_closed" eval="(DateTime.today() - relativedelta(months=3)).strftime('%Y-%m-%d %H:%M')"/>
             <field name="campaign_id" ref="utm.utm_campaign_email_campaign_products"/>
             <field name="source_id" ref="utm.utm_source_mailing"/>
             <field name="medium_id" ref="utm.utm_medium_email"/>