test: Remove REJECT message code
Summary:
We no longer use REJECT p2p message
This is backport of Core PR18609
Test Plan:
ninja check-functional-extended
grep -R on_reject test/functional/
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Differential Revision: https://reviews.bitcoinabc.org/D8920