remove now unneeded validation

lib/gitlab/ci/config/entry/job.rb

@@ -28,7 +28,6 @@ module Gitlab
               validates :allow_failure, boolean: true
               validates :parallel, numericality: { only_integer: true,
                                                    greater_than_or_equal_to: 2 }
-              validates :retry, hash_or_integer: true
 
               validates :when,
                 inclusion: { in: %w[on_success on_failure always manual delayed],