Well essential fatty acids are a good example for this. (Alpha-)linolenic acid was discovered sometime in the early 19th century and coined vitamin F since the the body can't synthesize the two molecules, but a few years later the view on this changed and EFA's lost their vitamin status. I'm not sure, but I think it's due to the amounts we need to consume they're simply classified as dietary fat instead.
As for other examples, I resorted to seeking wikipedia for this which has a nice list of ex-vitamins. That's my main source, so take this with a grain of salt!
Catechol was once considered to belong to the vitamer J along with riboflavin. It turned out the former isn't essential and therefore is not a vitamin, while the latter was reclassified as vitamin B2.
Others that didn't fit the profile due to either turning out to be synthesized by our bodies or not being as essential as originally assumed are vitamins B4, B8, O, U, L1 and L2.
Also, bioflavonoids were once considered vitamins (vitamin P), but aren't anymore. Not sure why that is, but they probably aren't essential either. It's still really good shit for lots of reasons, but they don't add to our sex appeal as they do for plants where they usually serve as pigments. EAT MOAR FLOWERS!
EDIT: My choice of words wasn't very good there. I said our understanding of the term "vitamin" has changed, but that's not really correct. The definition of the word hasn't changed, but what has changed are which molecules are classified as vitamins. The only time the actual definition of the word changed was when we realized that vitamins aren't all amines, only a few years after the term vitamine was first used.
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