test: Remove intermittently failing and not very meaningful BOOST_CHECK in cnetaddr_basic

Summary:
I noticed this test failure in our CI for an unrelated diff (D12170)

This is a backport of core#21689

Test Plan: ninja check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12175