configs: remove calao*_defconfig

The calao defconfigs no longer build with gcc 5.x, due to Linux kernel
versions used being too old. However, it is unlikely that anyone will
ever update them, since Calao Systems has gone bankrupt in April 2016.

Therefore, let's remove them. If anyone is interested again at some
point, it will be easy to revive them from the Git history.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>