posts: rework post deletion to use dialog box.

Rework post deletion from using a separate page to using a dialog box,
like flagging.

* Add `DELETE /posts/:id` endpoint.
* Remove `POST /moderator/post/posts/:id/delete` endpoint.

config/routes.rb

@@ -13,9 +13,7 @@ Rails.application.routes.draw do
     namespace :post do
       resources :posts, :only => [:delete, :expunge, :confirm_delete] do
         member do
-          get :confirm_delete
           post :expunge
-          post :delete
           get :confirm_move_favorites
           post :move_favorites
           get :confirm_ban
@@ -175,7 +173,7 @@ Rails.application.routes.draw do
   end
   resources :post_replacements, :only => [:index, :new, :create, :update]
   resources :post_votes, only: [:index]
-  resources :posts, only: [:index, :show, :update] do
+  resources :posts, only: [:index, :show, :update, :destroy] do
     resources :events, :only => [:index], :controller => "post_events"
     resources :replacements, :only => [:index, :new, :create], :controller => "post_replacements"
     resource :artist_commentary, :only => [:index, :show] do