[FIX] doc: clean exercise-dashboard xml to v8

Courtesy of Moises Lopez

Closes: #4336

doc/howtos/backend/exercise-dashboard

@@ -54,7 +54,6 @@ Index: addons/openacademy/views/session_board.xml
 +        <record model="ir.ui.view" id="board_session_form">
 +            <field name="name">Session Dashboard Form</field>
 +            <field name="model">board.board</field>
-+            <field name="type">form</field>
 +            <field name="arch" type="xml">
 +                <form string="Session Dashboard">
 +                    <board style="2-1">
@@ -90,6 +89,6 @@ Index: addons/openacademy/views/session_board.xml
 +            name="Session Dashboard" parent="base.menu_reporting_dashboard"
 +            action="open_board_session"
 +            sequence="1"
-+            id="menu_board_session" icon="terp-graph"/>
++            id="menu_board_session"/>
 +    </data>
 +</openerp>