We don't use or otherwise care about ptest for native recipes. Its therefore
pointless to take the performance hit for them and we can disable them.
(From OE-Core rev: f3d35bb4719d0b8f8e6fc5976e9dbfc0e2019c2e)
(From OE-Core rev: 16dd4cd5564a19b0a221661205430e01c35673af)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>