[FIX] web: kanban records' margins in mobile

There should not be any margin/padding in mobile mode.
Also remove useless rendering code of kanban view (this is the
renderer's job).

addons/web/static/src/js/views/kanban/kanban_view.js

@@ -13,7 +13,6 @@ var _lt = core._lt;
 
 var KanbanView = BasicView.extend({
     accesskey: "k",
-    className: "o_kanban",
     display_name: _lt("Kanban"),
     icon: 'fa-th-large',
     mobile_friendly: true,

addons/web/static/src/less/kanban_view.less

@@ -143,7 +143,7 @@
     overflow-x: visible;
 
     @media (max-width: @screen-xs-max) {
-        padding: 0px;
+        padding: 0px!important;
         overflow-x: auto;
     }
 
@@ -602,7 +602,7 @@
             margin: (@o-kanban-record-margin * 0.5) @o-kanban-record-margin;
 
             @media (max-width: @screen-xs-max) {
-                margin: 0 0 @o-kanban-record-margin 0;
+                margin: 0 0 -1px 0;
                 .o-flex(1, 0, 100%);
             }
 
@@ -632,8 +632,3 @@
     // Records colours
     .o-kanban-record-color();
 }
-
-// Introduced with new views (TODO check)
-.o_kanban {
-    height: 100%; // required for grouped kanban views
-}