enterprise-rhel-80-64-bit-large-txns-format

variant is running the tests with 

maxNumberOfTransactionOperationsInSingleOplogEntry: 2

parameter to test split transactions.
The tests were previously resistant to this, but the changes introduced (in the tests) with SERVER-78296 make them fail in that case.
 
As write_change_stream_pit_preimage_in_transaction.js tests already includes split transactions using large documents that don't fit into 16MB, we can safely remove it from this variant.
 
Additional work: A quick rework of the tests to clearly identify which preImages are in specific transactions would be great.