Toolbar: Remove unused .groups property
Toolbar: Remove unused .groups property

This is unused, even downstream. Also document that
a group object has to have a 'type'.

Change-Id: I3010d2e47c9e00ce288a0ec1cd5e95faa088b99f

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui