test: Remove unused classes from p2p_leak.py
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 [[https://github.com/bitcoin/bitcoin/pull/19727 | core#19727]]

Test Plan: `ninja check-functional`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

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

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