Upstream dropped support for GTK2 (in v3.1.0) and this flag was dropped.
Relevant upstream commit ID: 89d85cde75143325205e332dd97bf1bb8402d7c1
(From OE-Core rev: 90f5cf92c88d17ee976498a7f2b1d3514acb118b)
Signed-off-by: Chris Patterson <pattersonc@ainfosec.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>