Move chinese translation to localization-zh-cn-plugin

[yuezhuangshi]

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Since all localized files of Chinese has been independently formed as a plugin localization-zh-cn-plugin, so remove it from the repository and maintain future update in localization-zh-cn-plugin Please see: https://github.com/jenkinsci/jenkins/pull/4008 https://github.com/jenkinsci/localization-zh-cn-plugin/tree/master/plugins/credentials-plugin