test: Remove unused nVersion=1 in p2p tests

Summary:
After D9195 nVersion is no longer used in p2p logic when sending messages. Only when receiving
messages, but in this test no messages are received.

This is a backport of core#20131

Test Plan: ninja check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10501