Move @{sys} into tunables/kernelvars to make it readily available for
all profiles by default. In order to avoid duplicate variable
declaration, other tunable includes where modified accordingly.
Additionally, apparmor_api/is_enable has updated comment with regards to
@{sys} availability. tunables/sys is now marked as deprecated and should
not be used as it is noop, left only for backwards compatibility.
This is preparation for fixing bug:
https://bugs.launchpad.net/apparmor/+bug/1728551
Thanks to Christian Boltz for original idea to implement this in
non-breaking manner.
