setup/unixstyle-install: repair deletion on install merge

Repair a mistake in 4af9bf8.

Author: mflatt

racket/collects/setup/unixstyle-install.rkt

@@ -530,7 +530,8 @@
 (define (cleantree dst*)
   (define dst (if (symbol? dst*) (dir: dst*) dst*))
   (when (directory-exists? dst)
-    (printf "Deleting destination ~s...\n" dst)))
+    (printf "Deleting destination ~s...\n" dst)
+    (rm dst)))
 
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