[IMP] cron: remove useless pooljobs and schedule_cron_jobs methods

[IMP] cron: remove useless pooljobs and schedule_cron_jobs methods

The pooljobs and scheduled_cron_jobs stuff was only used to
delay the processing of cron jobs until after the registry
was fully loaded. However this is already the case because
RegistryManager.new() only sets the flag at the end of the
init step.
The flag was named `registry.cron` but simply meant that the
registry was fully loaded and ready, so it is simpler to
rename it to `registry.ready`.

In multiprocess mode this flag is enterily irrelevant
so there is no need to selectively set it to True or
False. `registry.ready` is simpler.

bzr revid: odo@openerp.com-20121221133751-h4x670vblfr3d09e