Ensure tracepoints are synchronized after unreg

Ensure tracepoints are synchronized after unreg

The tracepoint API provides tracepoint_synchronize_unregister() as a way
to guarantee that all tracepoint handlers are inactive.  This is
necessary after unregistering to allow the module to safely unload.

	* tapsets.cxx (tracepoint_derived_probe_group::emit_module_init):
	Call synchronize after unregistering tracepoints.
	(tracepoint_derived_probe_group::emit_module_exit): Ditto.