KillSessionsDuringPrepareDoesNotAbortTransaction tests a concurrent abort while a transaction is being prepared. After SERVER-38810, this test is not realistic, since an operation must check out the session in order to modify TransactionParticipant state, so a concurrent operation cannot abort a transaction while it is being prepared. However, this test is our only unit test coverage that abortTransactionIfNotPrepared() does not abort prepared transactions. It would be valuable to replace this test with a test that demonstrates abortTransactionIfNotPrepared() does not abort prepared transactions.