Remove ResourceId.getCurrentDirectory()?

Beam ResourceId currently has a getCurrentDirectory method that returns the current resource id if it's a directory, or the parent directory if it's a directory.

To implement this you need to know whether or not a particular path is a directory or not.

I'm trying to implement the Hadoop ResourceId implementation, and it's not clear if it's possible. Hadoop's Paths do not end a / if they are a directory (they are stripped), nor do hadoop paths tell you if something is a directory, so it's not possible to determine if a given path is a file that does not have a suffix, or a directory.

It's not clear to me that all file systems can determine whether a path is a directory and thus I don't believe it can be implemented reliably.

The only usages of getCurrentDirectory that I could find are in tests so it's not clear we actually need this.

I propose that we remove this method.

cc [~davor]

Imported from Jira [BEAM-2069](https://issues.apache.org/jira/browse/BEAM-2069). Original Jira may contain additional context.
Reported by: sisk.

Locate ResourceId.getCurrentDirectory and the test usages mentioned in the issue, then inspect the Hadoop ResourceId implementation and Hadoop Path behavior. Remove the method only if the usages can be retired; done means the API and affected tests no longer depend on directory inference.

Written by the indexing model from the issue text.