A few sharding js tests (such as merge_all_chunks_on_shard.js have to skip or alter the execution of specific test cases based on whether the logic is running under a suite with periodic CSRS stepdown events in background. 

The traditional way to do this was to check for the existence of the ContinuousStepdown class created by the override method, but after SERVER-79182, this is no more visible from a js test (unless the symbol gets explicitly imported).

Existing checks should hence be adapted to the introduction of ES modules into the code base.