As of opencontainers/runc@db093f6 runc no longer depends on libapparmor
thus libapparmor-dev no longer needs to be installed to build it or
anythind that depends on it (like containerd or cri-containerd). Adjust
the documentation accordingly.
containerd/containerd#2238 did the same for containerd.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>