glossary: Remove "leaf" and "hierarchy" from container namespace definition
glossary: Remove "leaf" and "hierarchy" from container namespace definition

Namespaces are not all hierarchical and processes aren't always in
leaves.

Signed-off-by: W. Trevor King <f75897670c17327c42ab201733fb8a81ff9f4c34@tremily.us>

opencontainers/specs,wking/opencontainer-runtime-spec,hqhq/specs,opencontainers/runtime-spec,wking/opencontainer-specs,laijs/specs,hqhq/runtime-spec