Removed post-SegWit activation test code from p2p-compactblocks (#2)

• Removed post-SegWit activation test code from p2p-compactblocks

All test nodes have been left. More understanding of the test design is needed
to determine whether any of them can be removed.

Only post-activation test steps have been removed, SegWit-dependent
functionality disabled.

The past passes, but more verification is needed to determine whether all
V2 CompactBlocks are indeed no longer transmitted during the test.

Where necessary, test nodes have been renamed to indicate that they are
no longer "segwit_node".

• Fix up invalid version (pick 999) and copyright

• Remove more segwit references, related method arguments