Currently, the creation path for timeseries collection is affected by SERVER-119866 bug.
The summary is that create collection in suites in which we have both rollback (stepdowns) + FCV upgrade/downgrade could lead to the creation of viewless timeseries collection when the legacy buckets collection already exists.

This was also surfaced by BF-41665.

For this reason we decided to disable the viewless timeseries feature flag from sharding_stepdown_fcv_upgrade_downgrade_jscore_passthrough until SERVER-119866 will be fixed.