Remove QUICK_TEST_SCENEGRAPH.

This is outdated (QSGView and friends are long gone) and not really needed given
that Qt 5 has its own copy of this code living in qtdeclarative.

Change-Id: I947366ce280a87c59c9e60f6665f8c6ab52b832f
Reviewed-by: Matthew Vogt <matthew.vogt@qinetic.com.au>