Remove dependency on OStatus2 gem (#12822)

Gemfile

@@ -68,7 +68,6 @@ gem 'nilsimsa', git: 'https://github.com/witgo/nilsimsa', ref: 'fd184883048b922b
 gem 'nokogiri', '~> 1.10'
 gem 'nsa', '~> 0.2'
 gem 'oj', '~> 3.10'
-gem 'ostatus2', '~> 2.0'
 gem 'ox', '~> 2.11'
 gem 'parslet'
 gem 'parallel', '~> 1.19'

Gemfile.lock

@@ -409,10 +409,6 @@ GEM
       omniauth (~> 1.3, >= 1.3.2)
       ruby-saml (~> 1.7)
     orm_adapter (0.5.0)
-    ostatus2 (2.0.3)
-      addressable (~> 2.5)
-      http (~> 3.0)
-      nokogiri (~> 1.8)
     ox (2.11.0)
     paperclip (6.0.0)
       activemodel (>= 4.2.0)

app/models/account.rb

@@ -314,10 +314,6 @@ class Account < ApplicationRecord
     self.fields = tmp
   end
 
-  def subscription(webhook_url)
-    @subscription ||= OStatus2::Subscription.new(remote_url, secret: secret, webhook: webhook_url, hub: hub_url)
-  end
-
   def save_with_optional_media!
     save!
   rescue ActiveRecord::RecordInvalid

spec/models/account_spec.rb

@@ -215,13 +215,6 @@ RSpec.describe Account, type: :model do
     end
   end
 
-  describe '#subscription' do
-    it 'returns an OStatus subscription' do
-      account = Fabricate(:account)
-      expect(account.subscription('')).to be_instance_of OStatus2::Subscription
-    end
-  end
-
   describe '#object_type' do
     it 'is always a person' do
       account = Fabricate(:account)