[FIX] sale: Display correclty 'Pro-forma #' on invoice report

Purpose
=======

When sending a proforma by email, the email template is correclty rendered. But 'Quotation #' id displayed on the printed report instead of 'Pro-forma' #

Specification
=============

- Retrieve correctly the context key in the template
- Remove the associated ir.actions.report.xml as we cannot pass a specific context from there

addons/sale/report/sale_report.xml

@@ -12,17 +12,5 @@
         <record id="report_sale_order" model="ir.actions.report.xml">
             <field name="print_report_name">(object.state in ('draft', 'sent') and 'Quotation'+'-'+(object.name) or 'Order'+'-'+(object.name))</field>
         </record>
-
-         <report
-            string="Pro-Forma"
-            id="report_proforma_quotation"
-            model="sale.order"
-            report_type="qweb-pdf"
-            name="sale.report_saleproforma"
-            file="sale.report_saleorder"
-        />
-        <record id="report_proforma_quotation" model="ir.actions.report.xml">
-            <field name="print_report_name">'Pro-Forma'+'-'+(object.name)</field>
-        </record>
     </data>
 </odoo>

addons/sale/report/sale_report_templates.xml

@@ -29,11 +29,11 @@
             </div>
 
             <h2>
-                <t t-if="not proforma">
+                <t t-if="not env.context.get('proforma', False)">
                     <span t-if="doc.state not in ['draft','sent']">Order # </span>
                     <span t-if="doc.state in ['draft','sent']">Quotation # </span>
                 </t>
-                <t t-if="proforma">
+                <t t-if="env.context.get('proforma', False)">
                     <span>Pro-Forma # </span>
                 </t>
                 <span t-field="doc.name"/>