[qa] Overhaul p2p_compactblocks.py
[qa] Overhaul p2p_compactblocks.py

Remove tests of:
 - compactblock behavior in a simulated pre-segwit version of bitcoind
   This should have been removed a long time ago, as it is not generally
   necessary for us to test the behavior of old nodes (except perhaps if we
   want to test that upgrading from an old node to a new one behaves properly)

 - compactblock behavior during segwit upgrade (ie verifying that network
   behavior before and after activation was as expected)
   This is unnecessary to test now that segwit activation has already happened.

Includes changes by John Newbery.

peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin