broker: unregister message handlers on exit

Problem: broker exits without freeing message handlers
associated with internal services.

Add broker_remove_service() to do this, and call it
from the broker exit path.

src/broker/broker.c

@@ -158,6 +158,7 @@ static void broker_handle_signals (broker_ctx_t *ctx, zlist_t *sigwatchers);
 static void broker_unhandle_signals (zlist_t *sigwatchers);
 
 static void broker_add_services (broker_ctx_t *ctx);
+static void broker_remove_services (void);
 
 static int load_module_byname (broker_ctx_t *ctx, const char *name,
                                const char *argz, size_t argz_len,
@@ -669,6 +670,7 @@ int main (int argc, char *argv[])
     hello_destroy (ctx.hello);
     attr_destroy (ctx.attrs);
     shutdown_destroy (ctx.shutdown);
+    broker_remove_services ();
     flux_close (ctx.h);
     flux_reactor_destroy (ctx.reactor);
     if (ctx.subscriptions) {
@@ -1743,6 +1745,13 @@ static void broker_add_services (broker_ctx_t *ctx)
         log_err_exit ("error registering message handlers");
 }
 
+/* Unregister message handlers
+ */
+static void broker_remove_services (void)
+{
+    flux_msg_handler_delvec (handlers);
+}
+
 /**
  ** reactor callbacks
  **/