Remove unused Account#magic_key (#11327)

app/models/account.rb

@@ -301,21 +301,6 @@ class Account < ApplicationRecord
     self.fields = tmp
   end
 
-  def magic_key
-    modulus, exponent = [keypair.public_key.n, keypair.public_key.e].map do |component|
-      result = []
-
-      until component.zero?
-        result << [component % 256].pack('C')
-        component >>= 8
-      end
-
-      result.reverse.join
-    end
-
-    (['RSA'] + [modulus, exponent].map { |n| Base64.urlsafe_encode64(n) }).join('.')
-  end
-
   def subscription(webhook_url)
     @subscription ||= OStatus2::Subscription.new(remote_url, secret: secret, webhook: webhook_url, hub: hub_url)
   end