Drop reserverd keywords from CoffeeScript.

Reserved words that can't be used in a language should not add
to its relevance.

Author: isagalaev

src/languages/coffeescript.js

@@ -19,9 +19,6 @@ function(hljs) {
       'true false null undefined ' +
       // Coffee literals
       'yes no on off',
-    reserved:
-      'case default function var void with const let enum export import native ' +
-      '__hasProp __extends __slice __bind __indexOf',
     built_in:
       'npm require console print module global window document'
   };