syntax/parse: fix disappeared-use property in attribute macro
syntax/parse: fix disappeared-use property in attribute macro

This fixes the DrRacket check syntax arrows in uses of `attribute` like this:
```racket
#lang racket/base
(require syntax/parse)
(syntax-parse #'a
  [a
   (attribute a)])
```

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket