Remove the introducer, which isn't being used anyway.

svn: r11692

collects/scheme/private/contract.ss

@@ -185,7 +185,6 @@ improve method arity mismatch contract violation error messages?
                            (car args))])))
 
 (define-syntax (with-contract stx)
-  (let ([introducer (make-syntax-introducer)])
   (syntax-case stx ()
     [(_ blame (arg ...) body0 body ...)
      (identifier? (syntax blame))
@@ -223,7 +222,7 @@ improve method arity mismatch contract violation error messages?
     [(_ blame bad-args body0 body ...)
      (raise-syntax-error 'with-contract
                          "expected list of identifier and/or (identifier contract)"
-			   #'bad-args)])))
+                         #'bad-args)]))
 
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