Clear all syntax subscriptions after spec runs

The global syntax object is reused between specs so
each spec should start off with a clean listener list.

spec/spec-helper.coffee

@@ -88,6 +88,7 @@ afterEach ->
   ensureNoPathSubscriptions()
   atom.pendingModals = [[]]
   atom.presentingModal = false
+  syntax.off()
   waits(0) # yield to ui thread to make screen update more frequently
 
 window.loadPackage = (name, options={}) ->