d/rules: Enable apparmor by default and drop debonf support

We don't need it and the current impl uses debconf as a registry which is shouldn't so drop that. Config file changes are picked up now while user changes are being preserved.

non modified case;

$ sudo dpkg -i flash-kernel_3.99pureos+libre5.3_arm64.deb
(Reading database ... 81690 files and directories currently installed.)
Preparing to unpack flash-kernel_3.99pureos+libre5.3_arm64.deb ...
Unpacking flash-kernel (3.99pureos+libre5.3) over (3.99pureos+libre5.3) ...
Setting up flash-kernel (3.99pureos+libre5.3) ...
Replacing config file /etc/default/flash-kernel with new version
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Processing triggers for man-db (2.8.5-2) ...

Closes: OS-issues#59 (closed)