[IMP] calendar: Avoid having no more filters

Before this commit:
In calendar view, when you unselect all filters of a category, all
events disappear (it's expected), but all filters also disappear.
So you can't selectd anything, you must reload the view to unlock
the situation.

After this commit:
When you unselect all filters of a category, all events disappear but
the filters stay as before selection (of course the last unselected
filter stay unselected).

closes odoo/odoo#44031

Taskid: 2146842
Related: odoo/enterprise#7970
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/web/static/src/js/views/calendar/calendar_model.js

@@ -595,10 +595,6 @@ return AbstractModel.extend({
                 return;
             }
 
-            _.each(filter.filters, function (filter) {
-                filter.display = !filter.active;
-            });
-
             var fs = [];
             var undefined_fs = [];
             _.each(events, function (event) {