Temporarily remove `instanceof` check for OrbitSourceClass
Temporarily remove `instanceof` check for OrbitSourceClass

Source inheritance in Orbit itself needs to be improved. This check is failing
for Ember > 1.5, although TBH, it doesn't seem like it should have been
working with Ember 1.3 either :/

pixelhandler/ember-orbit,pixelhandler/ember-orbit,opsb/ember-orbit,ProlificLab/ember-orbit,greyhwndz/ember-orbit,gnarf/ember-orbit,lytbulb/ember-orbit,orbitjs/ember-orbit,opsb/ember-orbit,ProlificLab/ember-orbit,gnarf/ember-orbit,orbitjs/ember-orbit,orbitjs/ember-orbit,lytbulb/ember-orbit,greyhwndz/ember-orbit,lytbulb/ember-orbit