Time for those old global jail sysctls to go

[James Gritton]

I've got a revision in the works <https://reviews.freebsd.org/D14791> to
remove the security.jail.foo_allowed sysctls:

> The old jail system had sysctls to set jail permissions for all jails
> (e.g. security.jail.mount_allowed), which were superseded by per-jail
> permissions (e.g. allow.mount). These old sysctls remain a constant
> source of confusion to users, who expect that setting the sysctl will
> change the behavior of existing jails. That the sysctl value at the 
> time
> a jail is created may matter is a backward-compatibility hack that does
> little or nothing to relieve the confusion. So it's time for them to 
> go.

> Also, jail(2) has been replaced by jail_set(2) for a number of years
> now, and it really ought to retire - at least into the COMPAT world.

This may be of interest to anyone who works with jails.  My hope is that
no current software relies on these old sysctls, and they can be removed
with little trouble.  But removing old things never seems to go that 
easy.

- Jamie