event_notifier: cleanups around event_notifier_set_handler

Remove the useless is_external argument.  Since the iohandler
AioContext is never used for block devices, aio_disable_external
is never called on it.  This lets us remove stubs/iohandler.c.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

stubs/Makefile.objs

@@ -35,6 +35,5 @@ stub-obj-y += kvm.o
 stub-obj-y += qmp_pc_dimm_device_list.o
 stub-obj-y += target-monitor-defs.o
 stub-obj-y += target-get-monitor-def.o
-stub-obj-y += iohandler.o
 stub-obj-y += pc_madt_cpu_entry.o
 stub-obj-y += migration-colo.o

stubs/iohandler.c

@@ -1,8 +0,0 @@
-#include "qemu/osdep.h"
-#include "qemu-common.h"
-#include "qemu/main-loop.h"
-
-AioContext *iohandler_get_aio_context(void)
-{
-    abort();
-}