Hi ,

Actually with view_mode, you need to delete the kanban view which is attached to the pipeline Action views. If you check with the record id "crm_lead_action_pipeline_view_kanban" , there is a action act window view which is linked with Pipeline Menu. So you need to unlink that view with view mode also 

just like :

            "For Pipeline Action"

        record model="ir.actions.act_window" id="crm.crm_lead_action_pipeline">
            field name="name">Pipeline
            field name="res_model">crm.lead
            field name="view_mode">tree,graph,pivot,form
            field name="domain">[('type','=','opportunity')]
            field name="context">{
                    'default_type': 'opportunity',
                    'search_default_assigned_to_me': 1
            }
            field name="search_view_id" ref="crm.view_crm_case_opportunities_filter"/>
        /record>

        "For Pipeline Kanban Action View"
        record id="crm.crm_lead_action_pipeline_view_kanban" model='ir.actions.act_window.view'>
            field name="sequence" eval="0"/>
            field name="view_mode">kanban
            field name="view_id" ref="crm.crm_case_kanban_view_leads"/>
            field name="act_window_id" eval="False"/>
        /record>

Hope it will help you, 
Thanks and Please vote up.