MM tables: fix (or disable) inferring buckets

The following tests on minimr produce diffs if all tables are changed to MM:

infer_bucket_sort_dyn_part
infer_bucket_sort_num_buckets
infer_bucket_sort_merge
infer_bucket_sort_reducers_power_two

Some of these disable strict checks for bucketing load, which wouldn't work by design; the rest should work. Either that, or we should disable this for MM tables - seems like an obscure feature.