tests/functional: remove comments talking about avocado

tests/functional: remove comments talking about avocado

The first comment is still relevant but should talk about our own test
harness instead. The second comment adds no value over reading the code
and can be removed.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20241121154218.1423005-8-berrange@redhat.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20241121165806.476008-8-alex.bennee@linaro.org>