test: Remove unused classes from p2p_leak.py

Summary:

test: remove CNodeNoVersionMisbehavior from p2p_leak.py

It's also clearer to have no_version_disconnect_node send a message
other than version or verack in order to reach the peer discouragement
threshold.

test: remove CNodeNoVersionIdle from p2p_leak.py

test: Distinguish between nodes(bitcoind) and peers(mininodes) in p2p_leak.py

Also, remove "C" prefix from class names to match new style

This is a backport of core#19727

Test Plan: ninja check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10117