DEV: Leaking state in PostActionNotifier in tests.

Follow-up to 8a0478b97d

app/services/post_action_notifier.rb

@@ -4,6 +4,7 @@ class PostActionNotifier
 
   def self.disable
     @disabled = true
+    @custom_post_revision_notifier_recipients = nil
   end
 
   def self.enable

spec/services/post_action_notifier_spec.rb

@@ -108,10 +108,6 @@ describe PostActionNotifier do
         end
       end
 
-      after do
-        DiscoursePluginRegistry.reset!
-      end
-
       it 'notifies the specified user of the revision' do
         expect {
           post.revise(evil_trout, raw: "world is the new body of the message")