test/build-utils.sh: remove support for Debian Jessie
test/build-utils.sh: remove support for Debian Jessie

Jessie is EOL since June 30, 2020, so it's probably fine to assume it's
no longer used.

https://www.debian.org/News/2020/20200709

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

dmcgowan/containerd,estesp/containerd,containerd/containerd,mikebrow/containerd,thaJeztah/containerd,thaJeztah/containerd,dmcgowan/containerd,mikebrow/containerd,estesp/containerd,containerd/containerd