This mainly removes no more needed glue code and fixes a recent
regression where the example set picker combobox on the Examples welcome
page always displayed the name of the first item, no matter which set
was displayed on the main canvas

Task-number: QTCREATORBUG-15727
Change-Id: I15b4c97f2e079a7470f6f63cde587dd4be58c40e
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>