[FIX] (portal_)project_issue: remove duplicated field

Field priority in kanban view was present twice which made inheritance harder

addons/portal_project_issue/portal_project_issue_view.xml

@@ -8,7 +8,6 @@
             <field name="priority">20</field>
             <field name="arch" type="xml">
                 <kanban class="oe_portal_project_issue">
-                    <field name="priority"/>
                     <field name="user_email"/>
                     <field name="user_id"/>
                     <field name="date_deadline"/>

addons/project_issue/project_issue_view.xml

@@ -191,7 +191,6 @@
                 <kanban default_group_by="stage_id">
                     <field name="stage_id"/>
                     <field name="color"/>
-                    <field name="priority"/>
                     <field name="user_email"/>
                     <field name="user_id"/>
                     <field name="date_deadline"/>