Minor ActivityPub JSON fixes (#4214)

- Objects must have attributedTo instead of actor
- The current attribute belongs to CollectionPage, not Collection

app/controllers/activitypub/outboxes_controller.rb

@@ -20,7 +20,6 @@ class ActivityPub::OutboxesController < Api::BaseController
     ActivityPub::CollectionPresenter.new(
       id: account_outbox_url(@account),
       type: :ordered,
-      current: account_outbox_url(@account),
       size: @account.statuses_count,
       items: @statuses
     )

app/controllers/follower_accounts_controller.rb

@@ -21,7 +21,6 @@ class FollowerAccountsController < ApplicationController
     ActivityPub::CollectionPresenter.new(
       id: account_followers_url(@account),
       type: :ordered,
-      current: account_followers_url(@account),
       size: @account.followers_count,
       items: @follows.map { |f| ActivityPub::TagManager.instance.uri_for(f.account) }
     )

app/controllers/following_accounts_controller.rb

@@ -21,7 +21,6 @@ class FollowingAccountsController < ApplicationController
     ActivityPub::CollectionPresenter.new(
       id: account_following_index_url(@account),
       type: :ordered,
-      current: account_following_index_url(@account),
       size: @account.following_count,
       items: @follows.map { |f| ActivityPub::TagManager.instance.uri_for(f.target_account) }
     )

app/controllers/tags_controller.rb

@@ -23,7 +23,6 @@ class TagsController < ApplicationController
     ActivityPub::CollectionPresenter.new(
       id: tag_url(@tag),
       type: :ordered,
-      current: tag_url(@tag),
       size: @tag.statuses.count,
       items: @statuses.map { |s| ActivityPub::TagManager.instance.uri_for(s) }
     )