configs: Remove udoo_quad_defconfig

configs/mx6udoo_defconfig supports the quad and dual-lite variants,
so there is no need to keep udoo_quad_defconfig anymore.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>