Remove old check for 3-byte shifted IP addresses from pre-0.2.9 node messages

Summary:
The change removes an old check for IPv6 addresses in range ::ff:ff00:0:0:0/72 that were created due to a bug in size field of addr messages for 0.2.8 nodes and before.

This check is no longer needed as they are no more pre 0.2.9 nodes on the network (as per bitnodes network snapshot).

Credits for discovering this go to sipa.

This is a backport of core#19797

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10134