Add remove from followers api (#16864)

* Add followed_by? to account_interactions

* Add RemoveFromFollowersService

* Fix AccountBatch to use RemoveFromFollowersService

* Add remove from followers API

app/models/concerns/account_interactions.rb

@@ -195,6 +195,10 @@ module AccountInteractions
     !following_anyone?
   end
 
+  def followed_by?(other_account)
+    other_account.following?(self)
+  end
+
   def blocking?(other_account)
     block_relationships.where(target_account: other_account).exists?
   end