We're not supporting Debian 9 anymore, and we are now testing
MinGW cross-compiler builds in the gitlab-CI, too, so we do not
really need these jobs in the shippable.yml anymore.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200921174320.46062-5-thuth@redhat.com>
Message-Id: <20200925154027.12672-13-alex.bennee@linaro.org>