Bug: comments are retained twice in the LLBC AST

[msprotz]

See https://github.com/AeneasVerif/eurydice/pull/238#issue-3237527798 -- if you look at https://github.com/AeneasVerif/symcrust/blob/68a3089dc215c62e0e6dcf3a6ddba2843bf119a6/c/symcrust_mlkem.c#L379-L383 there is a duplicated comment.

This comment appears twice in the LLBC AST (not a Eurydice issue). Looking at the source here https://github.com/AeneasVerif/symcrust/blob/0371b8667c11f44721b7db4c78cbe1d1ee7546db/src/ntt.rs#L673 I receive this comment at call-site for the "inner loop" function (the comment is attached to one of the parameters), in additional to the rightful place in the definition of the inner loop function.

Perhaps this has to do with our usage of a proc macro.