SERVER-93400 added a fsync call to timeseries_insert_mixed_schema_bucket.js and timeseries_update_mixed_schema_bucket.js. This was because background validate would read documents at the timestamp of the last stable checkpoint, and thus see timeseries mixed-schema buckets, yet observed the timeseries mixed-schema catalog flag at a later timestamp after it was disabled, and thus caused the validate to fail on an spurious inconsistency.

This fix is needed for older versions, but shouldn't be necessary for MongoDB v7.3+:

• The collMod is timestamped, and the timeseries mixed-schema flag is part of _mdb_catalog, so it can be read at a point in time.
• After SERVER-70779, background validate establishes a consistent view of the catalog and the documents at a point in time.

Remove the fsync calls to increase test coverage and simplify the code.