Summary:
I often find myself clicking the widget handle's {nav Remove} button and accidentally removing the widget itself when I'm just trying to hide the handle, because the button's current icon communicates "close this thing" better than "delete this thing". By switching it to a trash icon, we communicate its true meaning better and it becomes clear that the button will remove the widget.

This also brings that icon into consistency with the icon used in the context menu's {nav Remove this [widget]} entry.

Test Plan: {F6104676}

Reviewers: #plasma, #vdg, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: gregormi, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D14116