sets.extras: change non-repeating to use remove-first!.

extra/sets/extras/extras.factor

@@ -1,6 +1,6 @@
 ! Copyright (C) 2013 Doug Coleman.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: kernel locals sequences sets ;
+USING: kernel locals sequences sequences.extras sets ;
 IN: sets.extras
 
 : setwise-xor ( seq1 seq2 -- set )
@@ -23,5 +23,5 @@ IN: sets.extras
     0 seq new-resizable :> accum
     seq [
         accum over visited ?adjoin
-        [ push ] [ remove! drop ] if
+        [ push ] [ remove-first! drop ] if
     ] each accum seq like ;