Remove bt_ctf_stream_class_get_event_class_by_name()

Remove bt_ctf_stream_class_get_event_class_by_name()

CTF allows two event classes of the same stream class to have the same
name, but all event classes must have a unique ID. Remove
bt_ctf_stream_class_get_event_class_by_name() because this would need to
return a set of event classes, not just one, and this feature is not
strictly needed for the 2.0 target.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>