pg_archivecleanup docs

I think the documentation for the -x option is confusing:

-x extension

When using the program as a standalone utility, provide an extension
that will be stripped from all file names before deciding if they
should be deleted. This is typically useful for cleaning up archives
that have been compressed during storage, and therefore have had an
extension added by the compression program. For example: -x .gz.

This option behaves the same whether it is used as a standalone
utility or used by archive_cleanup_command. I don't think
pg_archivecleanup even knows how it is being called.

I think we should just strike the first clause.

Cheers,

Jeff