Revert "[FIX] web: hide dashboard tooltip on page change"

Mow that the Journal Dashboard use Chart.js, this patch is unneeded.

This reverts commit 6d9dabd5d9.

Oversight of previous forward-port.

addons/web/static/src/js/fields/basic_fields.js

@@ -2526,7 +2526,6 @@ var JournalDashboardGraph = AbstractField.extend({
      * Called when the field is detached from the DOM.
      */
     on_detach_callback: function () {
-        this.chart.tooltip.hidden(true);
         this._isInDOM = false;
     },