Rack implements `redirect?` so we don't need it

Rack [already implements `redirect?` on the response object](https://github.com/rack/rack/blob/1569a985e17d9caaf94d0e97d95ef642c4ab14ba/lib/rack/response.rb#L141) so we don't need to implement our own.

actionpack/lib/action_controller/test_case.rb

@@ -139,9 +139,6 @@ class LiveTestResponse < Live::Response
     # Was the URL not found?
     alias_method :missing?, :not_found?
 
-    # Were we redirected?
-    alias_method :redirect?, :redirection?
-
     # Was there a server-side error?
     alias_method :error?, :server_error?
   end

actionpack/lib/action_dispatch/testing/test_response.rb

@@ -16,9 +16,6 @@ def self.from_response(response)
     # Was the URL not found?
     alias_method :missing?, :not_found?
 
-    # Were we redirected?
-    alias_method :redirect?, :redirection?
-
     # Was there a server-side error?
     alias_method :error?, :server_error?
   end