buildroot

weston: drop --disable-xwayland-test

It's in the rpi backend block which makes no sense, and it depends on
xwayland being enabled which we currently don't support so remove it.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>