Ignore cppcheck error in EraseOrphanTx()

Summary:
This is an unusual case where another container is actually tracking
the iterator of another container. cppcheck iterators1 is clearly useful,
so we do not want to disable it entirely. Instead, we can simply ignore this
one case.

Test Plan: arc lint net_processing.cpp is green after this patch

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6873