Mark all Apport related entries as NFU

src:apport itself was ever only in experimental and never migrated to
unstable as it needed extra services to actually function.

Maintainer recently asked for complete removal of Apport, tracked as
https://bugs.debian.org/924960 .

As it was never in unstable or any other supported suites, we can mark
it safely as NFU considering it was never in Debian.