As part of
SERVER-32635, a last-stable binary version mongos will crash upon attempting to connect to a latest featureCompatibilityVersion cluster. However, since this behavior was added for 4.0 mongos and FCV 4.2 was not present at the time, some special testing behavior was necessary to simulate a 4.0 mongos crashing. As part of the 4.2 upgrade/downgrade work, the crash_mongos_against_upgraded_cluster.js test should be updated to no longer rely on these failpoints and just directly use a 4.0 mongos and FCV 4.2 cluster. The failpoints/wireVersion added as part of SERVER-32635 solely for simulation of the crash should also be removed.