B-77841 - Create a filter that redacts private attributes

- The filter current references /etc/repose/usage-schema/rm_private_attrs_for_obs.xsl which is installed through usage-schema
Also, the rm_private_attr_for_obs.xsl does not have a unit test in standard-usage-schemas. :-( Because previously it was an XSLT for Repose and it's hard to write a unit test for Repose Translation Filter. But now that the XSLT is being invoked in our filter, I think it would be good to add a unit test for it. Would this be a good story for our new guys?