Is the term 'Occidental' still in common usage - or is it a legacy of a bygone age?

Occident is the antonym of orient, not a synonym.

Oc·ci·dent
noun \ˈäk-sə-dənt, -ˌdent\
: west
(from sunset)

Occident is not "used to mean the same as Oriental". However, the word is very rarely used, and today, it is mostly limited to sense of the Western World.

This ngram shows the limited and declining use or the words. Notice oriental itself steeply falling in recent years.

1950-2008: occident,occidental,orient,oriental Occident,Occidental,Orient,Oriental,OCCIDENT,OCCIDENTAL,ORIENT,ORIENTAL

Those terms are used in traditional astrology: for the planets in horary charts, and sometimes in natal chart interpretation. Oriental planet is the planet which rise on the horizont before sun. Occidental planet rise on the horizont after the sun. There is another definiton from Ptolomy, but it is purely astrological and it considers geometrical division of the natal chart.