remove old comment

lib/remark-mention.js

@@ -1,9 +1,5 @@
 import findAndReplace from 'mdast-util-find-and-replace'
 
-// Username may only contain alphanumeric characters or single hyphens, and
-// cannot begin or end with a hyphen*.
-//
-// \* That is: until <https://github.com/remarkjs/remark-github/issues/13>.
 const userGroup = '[\\w_]+'
 
 const mentionRegex = new RegExp(