Change check orphaned event to callback event

The orphaned event is quite strange, looks like a
execution-bug-selfcheck-and-heal event, which checks if checks hasn't
been executed, and thus reschedule them, something like if a host or
service check has been forgotten.

Anyway, this isn't about cleaning up the check exeuction code, so keep
the event as is, but execute it through callbacks so we can get rid of
that dependency from events.c to checks.c

Signed-off-by: Max Sikstrom <msikstrom@op5.com>