Re-enable tst_QJSEngine::stringObjects test
Re-enable tst_QJSEngine::stringObjects test

Corresponding bug has been fixed in QtJSBackend thus re-enable test and
remove expected failures.

Change-Id: I72d6ce31a1c932db29dad0758e0c2654543a5b1f
Reviewed-by: Simon Hausmann <a975102812d593b3191088e3d0aeaeb6f11dbcf5@digia.com>

corngood/qtdeclarative,crobertd/qtdeclarative,qmlc/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,crobertd/qtdeclarative,jfaust/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,crobertd/qtdeclarative,corngood/qtdeclarative,crobertd/qtdeclarative,jfaust/qtdeclarative,matthewvogt/qtdeclarative,corngood/qtdeclarative,mgrunditz/qtdeclarative-2d,matthewvogt/qtdeclarative,crobertd/qtdeclarative,corngood/qtdeclarative,qmlc/qtdeclarative,corngood/qtdeclarative,mgrunditz/qtdeclarative-2d,jfaust/qtdeclarative,crobertd/qtdeclarative,corngood/qtdeclarative,matthewvogt/qtdeclarative,jfaust/qtdeclarative,crobertd/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,corngood/qtdeclarative,matthewvogt/qtdeclarative,qmlc/qtdeclarative,matthewvogt/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,matthewvogt/qtdeclarative,mgrunditz/qtdeclarative-2d,jfaust/qtdeclarative,jfaust/qtdeclarative,jfaust/qtdeclarative