Remove delay when hitting Reply... button on page with a lot of comments

Every time the "Reply..." button was hit, a new GLForm was instantiated (which is fine), which would then call GitLab.GfmAutoComplete.setup() without specifying which textarea we needed autocompletion on, which resulted in GitLab.GfmAutoComplete.setup iterating through every single textarea on the page. On a page with a lot of comments, where each comment would have its own textarea that will be used to edit the comment, this would take a long time and cause the whole page to hang for 2 seconds when a "Reply..." button was clicked.