Bug 1351074 followup, touch CLOBBER to really get AsyncSpellCheckTestHelper.jsm removed

CLOBBER

@@ -22,4 +22,4 @@
 # changes to stick? As of bug 928195, this shouldn't be necessary! Please
 # don't change CLOBBER for WebIDL changes any more.
 
-Bug 1351604 - required because DER.jsm and X509.jsm are no longer shipped with the browser
+Bug 1351074 - required because bug 1352982 means removing a .jsm requires a clobber