apparmor: change how profile replacement update is done

remove the use of replaced by chaining and move to profile invalidation
and lookup to handle task replacement.

Replacement chaining can result in large chains of profiles being pinned
in memory when one profile in the chain is use. With implicit labeling
this will be even more of a problem, so move to a direct lookup method.

Signed-off-by: John Johansen <john.johansen@canonical.com>