Properly delete remote account's avatar/header when fetch/update (#18973)

app/services/activitypub/process_account_service.rb

@@ -105,11 +105,13 @@ class ActivityPub::ProcessAccountService < BaseService
   def set_fetchable_attributes!
     begin
       @account.avatar_remote_url = image_url('icon') || '' unless skip_download?
+      @account.avatar = nil if @account.avatar_remote_url.blank?
     rescue Mastodon::UnexpectedResponseError, HTTP::TimeoutError, HTTP::ConnectionError, OpenSSL::SSL::SSLError
       RedownloadAvatarWorker.perform_in(rand(30..600).seconds, @account.id)
     end
     begin
       @account.header_remote_url = image_url('image') || '' unless skip_download?
+      @account.header = nil if @account.header_remote_url.blank?
     rescue Mastodon::UnexpectedResponseError, HTTP::TimeoutError, HTTP::ConnectionError, OpenSSL::SSL::SSLError
       RedownloadHeaderWorker.perform_in(rand(30..600).seconds, @account.id)
     end