change_stream_enforce_max_time_ms_on_mongos.js expects getMore to schedule follow-up getMores

The test issues a getMore with a maxTimeMS of 500, and expects this command to schedule getMores on each of the shards. After SERVER-34204 this is no longer the case, since the subsequent getMores may be delayed until the next getMore comes in.

We should re-write the test to account for this possibility, or we should add a unit test for this behavior and delete the assertions from the javascript test.