Revert "[FIX] web: empty kanban view on mobile"

Original commit breaking kanban view: 4cd379cf
Commit reverted: 287136b8

Two fixes were added independently to fix this bug but only one is needed.

odoo/enterprise@c8fe86fa225d3a5967e629f8fd35e1c92aa1fa61 best fix
287136b8 other fix (now reverted)

Reverting this commit fix the following bugs:
- Swipe on kanban : Not able to swipe on empty column. it only works on cards
- Popup activity on kanban card is unusable
- On kanban separation, "Undefined" cards are before the kanban separation

closes odoo/odoo#30177