Fix duplicate model find query in UploadsController

UploadsActions memoizes the result of `#find_model` in `#model`. That
means that if we call `#find_model` first, we'll run the query twice. As
`#model` is memoized, we don't need the `before_action` at all anyway.

app/controllers/uploads_controller.rb

@@ -20,7 +20,7 @@ class UploadsController < ApplicationController
 
   skip_before_action :authenticate_user!
   before_action :upload_mount_satisfied?
-  before_action :find_model
+  before_action :model
   before_action :authorize_access!, only: [:show]
   before_action :authorize_create_access!, only: [:create, :authorize]
   before_action :verify_workhorse_api!, only: [:authorize]