UBUNTU: [Packaging] Drop the processing of perm-blacklist

UBUNTU: [Packaging] Drop the processing of perm-blacklist

perm-blacklist lists modules and/or symbols that are permanently excluded
from the ABI check. AFAICT this hasn't been used in ages and with the
previous commit it would move up one level which puts it outside of the
ABI directory. That in itelf is not problematic just not pretty. Take this
opportunity to get rid of the whole (unsued) concept. We can always add it
back later should the need arise (and then should probably rename it to
abi.perm-blacklist to make it clear that it's a file related to the ABI).

Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>