Clean modeling utils, linked to  #17760 and #17713
# What does this PR do?
The recently introduced `TF` and `FLAX` sharding scripts #17760 and #17713 both use ` convert_file_size_to_int, get_checkpoint_shard_files`, which were moved to `transformers.utils.hub`. This PR just removed the definition of these two function and imports them form `transformers.utils.hub` 
_The documentation is not available anymore as the PR was closed or merged._