[server] remove cnxset tracking, it is now unneeded Indeed, all cnxsets will now be acquired using the following API:: with session.new_cnx() as cnx: cnx.execute(...) # do stuff cnx.commit() These well-scoped blocks are the only place a cnxset can be acquired. The old use-case for un-delimited cnxsets (pyro/zmqpickle protocols) have been removed. The "mode" of connection objects becomes "write" forever (it will be removed in a couple of changesets). Related to #2919309.

[devtools] remove the remaining bw compat for old-style tests It is just: * dangerously untested right now * on the path of further bw compat removal (cnxset handling) webtest drops an apparently pointless .login call Related to #3933480.