Use the new ucscPersonIsPostDoc attribute to display postdocs

[kanarb]

Hi Kumar. I think we do want to change from using a filter (ucscpersonpubstafftype=Postdoctoral Scholar) to using the new attribute (ucscPersonIsPostDoc) for the following reason, which Krishna explains in INC1522478:

If a user has a postdoc position (per their job code in UCPath) but has not updated their campus directory profile to reflect that.....they would not be included when filtering for (ucscpersonpubstafftype=Postdoctoral Scholar).

Since what we have now is working okay, I think we can consider this a low priority enhancement.