[racket] disappeared-use syntax property

Is it 'wrong' to add a disappeared-use property onto a syntax object
even if the use wasn't actually disappeared? Its not very obvious what
semantics these syntax properties are supposed to have.

The situation I'm in is that the code that determines examines the
bindings is somewhat separate from the code that finally makes the
decision on whether or not to remove the use. So if it was ok to
unconditionally add any identifier whose binding matched the first
step, that would be useful.