approvals: move post approval endpoint to /post_approvals.

Move the post approval endpoint from `POST /moderator/post/approval` to
`POST /post_approvals`.

test/functional/moderator/post/approvals_controller_test.rb

@@ -1,25 +0,0 @@
-require 'test_helper'
-
-module Moderator
-  module Post
-    class ApprovalsControllerTest < ActionDispatch::IntegrationTest
-      context "The moderator post approvals controller" do
-        setup do
-          @admin = create(:admin_user)
-          as_admin do
-            @post = create(:post, :is_pending => true)
-          end
-        end
-
-        context "create action" do
-          should "render" do
-            post_auth moderator_post_approval_path, @admin, params: {:post_id => @post.id, :format => "js"}
-            assert_response :success
-            @post.reload
-            assert(!@post.is_pending?)
-          end
-        end
-      end
-    end
-  end
-end