[FSDP] Added deprecation msg for `NO_SHARD` (#119553)
This only includes the warning for world size >1 since we clamp to `NO_SHARD` for world size 1. We mainly do not want `NO_SHARD` to proliferate anymore.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119553
Approved by: https://github.com/Skylion007
