Handle instrument target in trace_ust_create_event()

Copy instrument target and probe information from client.

Free allocated instrument target data when destroying events.

Also remove unused LTTNG_EVENT_FUNCTION_ENTRY event type.
Handle instrument target in trace_ust_find_event()

Add instrument target as a ltt_ust_ht_key and handle it in function
trace_ust_ht_match_event() and add_unique_ust_event().