Remove Buffer.proto.getMode. All ace interaction should be mediated by LanguageMode

src/app/buffer.coffee

@@ -164,22 +164,6 @@ class Buffer
   isModified: ->
     @modified
 
-  getMode: ->
-    return @mode if @mode
-    extension = if @getPath() then @getPath().split('/').pop().split('.').pop() else null
-    modeName = switch extension
-      when 'js' then 'javascript'
-      when 'coffee' then 'coffee'
-      when 'rb', 'ru' then 'ruby'
-      when 'c', 'h', 'cpp' then 'c_cpp'
-      when 'html', 'htm' then 'html'
-      when 'css' then 'css'
-      when 'java' then 'java'
-      when 'xml' then 'xml'
-      else 'text'
-
-    @mode = new (require("ace/mode/#{modeName}").Mode)
-
   matchesInCharacterRange: (regex, startIndex, endIndex) ->
     text = @getText()
     matches = []