lava: Remove any old comment on Minnowboard

The lava test templates have some comments on the timeouts referring to
the Minnowboard, now retired. Let's remove this old comments, but keep
the used timeouts, as that's the current setup working on LAVA.

A follow up task should revisit these timeouts and set them more tightly
if needed.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>