Remove the last dregs of trapframe_t.  It turns out only arm was using
this type, so remove it to make arm code more consistant with other
platforms.  Thanks to bde@ for pointing out only arm used trapframe_t.
Include lock.h before mutex.h.
Almost all if_clone consumers do not care about if_clone_event.
Do not force them to include sys/eventhandler.h. Those who
utilize EVENTHANDLER(9), will see the declaration.