Reduce usage of LD signatures (#9659)

* Do not LDS-sign Follow, Accept, Reject, Undo, Block

* Do not use LDS for Create activities of private toots

* Minor cleanup

* Ignore unsigned activities instead of misattributing them

* Use status.distributable? instead of querying visibility directly

app/services/follow_service.rb

@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
 class FollowService < BaseService
-  include StreamEntryRenderer
-
   # Follow a remote user, notify remote user about the follow
   # @param [Account] source_account From which to follow
   # @param [String, Account] uri User URI to follow in the form of username@domain (or account record)
@@ -82,10 +80,10 @@ class FollowService < BaseService
   end
 
   def build_json(follow_request)
-    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
+    ActiveModelSerializers::SerializableResource.new(
       follow_request,
       serializer: ActivityPub::FollowSerializer,
       adapter: ActivityPub::Adapter
-    ).as_json).sign!(follow_request.account))
+    ).to_json
   end
 end