Merge branch '19075-new-wiki' into 'master'

Remove duplicate new page btn from edit wiki

## What does this MR do?
Removes duplicate button on wiki page

## What are the relevant issue numbers?
Closes #19075

## Screenshots (if relevant)
![Screen_Shot_2016-06-24_at_9.45.28_AM](/uploads/8dca96c3e75b428d63acaaba6dede9a6/Screen_Shot_2016-06-24_at_9.45.28_AM.png)
![Screen_Shot_2016-06-24_at_9.45.57_AM](/uploads/e6ea97b07e48d2fe6f108d8c5a943583/Screen_Shot_2016-06-24_at_9.45.57_AM.png)

See merge request !4904
(cherry picked from commit 121c5c83)

app/views/projects/wikis/edit.html.haml

@@ -15,9 +15,10 @@
         Edit Page
 
     .nav-controls
-      - if can?(current_user, :create_wiki, @project)
-        = link_to '#modal-new-wiki', class: "add-new-wiki btn btn-new", "data-toggle" => "modal" do
-          New Page
+      - if !(@page && @page.persisted?)
+        - if can?(current_user, :create_wiki, @project)
+          = link_to '#modal-new-wiki', class: "add-new-wiki btn btn-new", "data-toggle" => "modal" do
+            New Page
       = render 'main_links'