Reintroduce the build dependency on dh-apparmor

During the rebase the build dependency introduced with the 023d3fb0 "Add dh-apparmor as build-deps" commit got lost, causing the build to fail with:

dh_apparmor -pdlt-daemon --profile-name=usr.bin.dlt-daemon
make[1]: dh_apparmor: No such file or directory
make[1]: *** [debian/rules:30: override_dh_installinit] Error 127
make[1]: Leaving directory '/usr/src/packages/BUILD'
make: *** [debian/rules:18: binary] Error 2
dpkg-buildpackage: error: fakeroot debian/rules binary subprocess returned exit status 2