apparmor: switch to apparmor to internal capable check for policy management

With LSM stacking calling back into capable to check for MAC_ADMIN
for apparmor policy results in asking the other stacked LSMs for
MAC_ADMIN resulting in the other LSMs answering based on their
policy management.

For apparmor policy management we just need to call apparmor's
capability fn directly.

Signed-off-by: John Johansen <john.johansen@canonical.com>