Cleanup person_by_handle route

I think this is a leftover from a long time ago and I can't find
anything that still uses that

closes #8280

app/controllers/people_controller.rb

@@ -113,15 +113,6 @@ class PeopleController < ApplicationController
     end
   end
 
-  def retrieve_remote
-    if params[:diaspora_handle]
-      Workers::FetchWebfinger.perform_async(params[:diaspora_handle])
-      head :ok
-    else
-      head :unprocessable_entity
-    end
-  end
-
   private
 
   def find_person

config/routes.rb

@@ -181,10 +181,6 @@ Rails.application.routes.draw do
     resources :photos, except:  %i(new update)
     get :stream
     get :hovercard
-
-    collection do
-      post 'by_handle' => :retrieve_remote, :as => 'person_by_handle'
-    end
   end
 
   # Note: The contraint for this route's username parameter cannot be removed.