Mac: Re-enable qcamerabackend test

The cause of the tests flakyness has been resolved, so it should be
re-enabled.

Task-number: QTBUG-36040
Change-Id: Ic4d18ea891ed5b6c5f4acbb4d05322b910b87d29
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

tests/auto/integration/qcamerabackend/qcamerabackend.pro

@@ -9,4 +9,3 @@ CONFIG += testcase
 SOURCES += tst_qcamerabackend.cpp
 DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0
 
-mac: CONFIG += insignificant_test # QTBUG-36040