apparmor: cleanup remove unused percpu critical sections in buffer management

apparmor: cleanup remove unused percpu critical sections in buffer management

There are two unused percpu critical sections in the buffer management
code. These are remanents from when a more complex hold algorithm was
used. Remove them, as they serve no purpose.

Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>