cpg: Add more comments to notify_lib_joinlist

And make handling of left_list more generic. Also free skiplist
allocated by joinlist_inform_clients function. Last (but not least)
remove czechlish founded (should have been pp of "find").

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>