Revert "Just use the already existing change grammar event."

This reverts commit 9014634b3a.

src/text-editor.coffee

@@ -323,6 +323,9 @@ class TextEditor extends Model
   onDidChangeGrammar: (callback) ->
     @emitter.on 'did-change-grammar', callback
 
+  onDidUseGrammar: (callback) ->
+    @displayBuffer.onDidUseGrammar(callback)
+
   # Extended: Calls your `callback` when the result of {::isModified} changes.
   #
   # * `callback` {Function}