thorium: add message:worker_pool_dequeue tracepoint

tracepoint message:actor_send 1140947676929850 ns
tracepoint message:worker_send 1140947676929927 ns (+ 77 ns)
tracepoint message:worker_send_mailbox - ns
tracepoint message:worker_send_schedule - ns
tracepoint message:worker_enqueue_message 1140947676930142 ns (+ 215 ns)
tracepoint message:worker_dequeue_message 1140947688365462 ns (+ 11435320 ns)
tracepoint message:worker_pool_dequeue 1140947688365509 ns (+ 47 ns)
tracepoint message:node_send 1140947688365558 ns (+ 49 ns)
tracepoint message:node_send_system 1140947688365846 ns (+ 288 ns)
tracepoint message:transport_send - ns
tracepoint message:transport_receive - ns
tracepoint message:node_receive - ns
tracepoint message:worker_receive 1140947688366827 ns (+ 981 ns)
tracepoint message:actor_receive 1140947688368069 ns (+ 1242 ns)

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>