- Delete config/appsignal.exs (was never wired into mix.exs or any
other config file)
- Migration: fix decrement_packet_sequence trigger to handle the case
where currval() hasn't been called in the current DB session, matching
the same exception handling already present in get_packet_count()
- Fix get_historical_packet_count test: invalid non-list bounds are
silently ignored (no error), so assert is_integer not count == 0
- Add Repo.delete_all(Packet) setup blocks in PacketsOldestTest and
PacketConsumerTest to clear any committed DB state before tests that
depend on an empty packets table
