Fix #4973: Wiki pages json index returns 404.

Fix regression introduced in 0db20e0ca. Setting `format: false` on the
wiki pages resource disabled format negotiation on all wiki page routes,
not just the show page, which meant /wiki_pages.json no longer worked.

The fix to monkey patch the internal Rails method that parses the file
extension from the URL, and have it ignore everything but the .html,
.json, .js, and .xml extensions. This is really hacky and may break in
future Rails releases.

app/controllers/wiki_pages_controller.rb

@@ -30,15 +30,6 @@ class WikiPagesController < ApplicationController
   end
 
   def show
-    if params[:format].present?
-      request.format = params[:format]
-    elsif params[:id].ends_with?(".html", ".json", ".xml")
-      request.format = params[:id].split(".").last
-      params[:id].delete_suffix!(".#{request.format.symbol}")
-    else
-      request.format = "html"
-    end
-
     @wiki_page, found_by = WikiPage.find_by_id_or_title(params[:id])
 
     if request.format.html? && @wiki_page.blank? && found_by == :title