We didn't. Oh sure, there are still nationalists in Japan who think that way ... just like there are neo-Nazis in Germany despite the appropriately-draconian de-Nazification program enacted during the occupation. But they are relatively few and far between.
The process of tearing down the God-Emperor began almost immediately, when Hirohito was pretty much ordered to pay a social call on Douglas MacArthur (as opposed to the other way around). The result was one of the classic photographs of the 20th Century, one that - by intent - diminished the Emperor and helped the Japanese along in viewing the Emperor as the figurehead/symbolic representation of the state that he remains today:
