Remove QtJSBackend_dev_Integration CI.

qtjsbackend#dev is not used anymore after the wip/v4 branch
was merged into qtdeclarative#dev

Change-Id: I2567452208b0df75c1dd0757ce3ce5929131a482
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>