Serialize ActivityPub alternate link into OStatus deletes, handle it (#4730)

Requires moving Atom rendering from DistributionWorker (where
`stream_entry.status` is already nil) to inline (where
`stream_entry.status.destroyed?` is true) and distributing that.

Unfortunately, such XML renderings can no longer be easily chained
together into one payload of n items.

spec/services/batched_remove_status_service_spec.rb

@@ -48,11 +48,10 @@ RSpec.describe BatchedRemoveStatusService do
     expect(Redis.current).to have_received(:publish).with('timeline:public', any_args).at_least(:once)
   end
 
-  it 'sends PuSH update to PuSH subscribers with two payloads united' do
+  it 'sends PuSH update to PuSH subscribers' do
     expect(a_request(:post, 'http://example.com/push').with { |req|
-      matches = req.body.scan(TagManager::VERBS[:delete])
-      matches.size == 2
-    }).to have_been_made
+      matches = req.body.match(TagManager::VERBS[:delete])
+    }).to have_been_made.at_least_once
   end
 
   it 'sends Salmon slap to previously mentioned users' do