Fix: probes should be compared strictly by events metadata

Currently, events are compared using names and signatures. Events
with different payloads but identical name and signatures could
lead to corrupted trace because the Session Daemon would consider them
identical and give them the same event ID.

Events should be compared using the name, loglevel, fields and
model_emf_uri to ensure that their respective metadata is the same.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>