FileSystems contract rename/delete to allow prior partial successes to make continued progress

The [filesystems contract](https://docs.google.com/document/d/11TdPyZ9_zmjokhNWM3Id-XJsVG3qel2lhdKTknmZ_7M/edit#heading=h.kpqagzh8i11w) for delete/rename say that an error should be raised if the resources don't exist.

I believe the contract should be updated to not have failures if the resources don't exist as we want them to be retried on failure without needing the caller know that a prior call may have been partially successful.

Imported from Jira [BEAM-5425](https://issues.apache.org/jira/browse/BEAM-5425). Original Jira may contain additional context.
Reported by: lcwik.