Bug 520165 followup - take the magic number out of the test_autocomplete.js change

toolkit/components/satchel/test/unit/test_autocomplete.js

@@ -61,7 +61,7 @@ function getFormExpiryDays () {
     if (prefs.prefHasUserValue("browser.formfill.expire_days"))
         return prefs.getIntPref("browser.formfill.expire_days");
     else
-        return 180;
+        return DEFAULT_EXPIRE_DAYS;
 }
 
 function run_test() {