Clean up separated ban/discourage interface

Summary:
This completes the backport of Core PR19219, the last commit being delayed due to missing
dependant backports.

https://github.com/bitcoin/bitcoin/pull/19219/commits/2ad58381fffb33d611abf900b73d9e6b5a4e35f8

Test Plan:

ninja check check-functional

cmake -GNinja .. -DENABLE_SANITIZERS="address;fuzzer" -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
ninja bitcoin-fuzzers
./src/test/fuzz/addrdb

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7146