Expel from Billy Bunter's form (6)

I believe the answer is:

remove

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'bunter's form' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for remove that I've seen before include "Take away from present place, or get rid of" , "class in school" , "Transfer, detach" , "Subtract" , "Expel" .)

I've seen this clue in the Evening Standard.

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